Most child seats are suitable for children between the ages of about nine months and four years. The lower limit is dependent on the ability of your child to sit up unsupported – that is, on the floor rather than propped up with cushions.
Some seats recline and children as young as six months – those who can sit up when propped up – can go in those. A reclining seat is better anyway because it allows your little one to drift off to sleep without slumping sideways or forwards.
The upper limit is restricted by weight rather than age. Seats are typically rated for passengers weighing up to around 20kg (44lb). Even if a seat seems sturdy enough to take a heavier child than that, it’s a bad idea to exceed its weight limit. It’s not so much that the seat will break – although it might – rather that the handling of the bike gets progressively worse with a heavier passenger, particularly with a rear-fitting seat.
How many children?
It’s possible to use front and rear seats on the same bike, but unless you live somewhere flat, doing so makes the bike very cumbersome. A child trailer is a superior solution for two children.
If you need just the one seat, then, despite its handling quirks, the pedalling and safety advantages of a rear seat make it the better option.
Rear seats come in three basic designs: cantilevered from the seat tube; fixed to a rear carrier rack; and fixed directly to the seat tube and seat stays. Those that bolt to the frame – or to a rack that’s bolted to the frame – are more stable and sturdy but cannot be fitted to bikes with rear suspension.
Cantilevered seats use a big plastic bracket with two holes in it bolted to the seat tube. Into this slots a two-pronged rack that supports the seat. There’s some give in the rack, which offers a degree of springy suspension. This may not flex enough under smaller children, leaving them tipped slightly forwards.
Larger children and/or long-term use may flex it too far, bending it down towards the rear tyre or mudguard. Typically the more you pay, the sturdier the seat will be. The Hamax Sleepy  and the Hamax Siesta  are some of the better examples. They have a decent attachment bracket and the seat can be reclined.
Seats that fix to a rear carrier rack slide and lock onto the rack’s top, with a safety strap around the seat-post or seat-tube for added security. With the seat off, the rack can be used to carry panniers. The Copilot Limo  is the best of these designs and has for some years set the standard in child seats.
The Limo reclines to give a better ride to a sleeping child. Its harness is supplemented by a pivoting grab-bar, like the safety bar on a roller-coaster carriage. What’s more, you can rotate this bar over the back of the seat to turn it into a baby chair when it’s off the bike – so you don’t need to wake your sleeping tot at journey’s end.
Seats that fix directly to the seat stays and seat tube have long legs that bolt to the seat stays, often using a quick-release, plus a bracket that fits on the seat tube to prevent fore and aft movement. The Bobike Maxi  is a good one. It’s well made, with a maximum load of 25kg. That should be enough for a six-year-old child, assuming you can still balance the bike properly.
Most seats fit best on medium or larger sized bikes with a conventional top tube. Small frames and those with a dropped top tube can cause fitting difficulties for any seat that uses a seat tube bracket. Open frames – that is, frames without a top tube – can flex and shimmy alarmingly when you’re cycling with a heavier child on a rear seat, because the structure isn’t stiff enough. Look for fatter frame tubes and/or reinforcing tubes if you want to fit this kind of bike with a child seat.
Front seats usually attach to the top tube, a bar fixed above it, or a bracket on the head tube. Some are moulded plastic seats, like smaller versions of rear seats, while others – aimed at older children who can hold on themselves – are just little saddles and footrests bolted to the bike.
- Front seat have the advantage that your child can see more and can talk to you more easily.
- In the event of a fall, or if you brake suddenly your child can end up acting as your airbag.
- You may end up pedalling awkwardly with your knees out, but balance is actually better, particularly over bumps.
- Your child is slightly more exposed to wind chill.
- Those little saddles that bolt to the top tube aren’t recommended for anything other than short journeys. A tired child could slip sideways or let a foot dangle into the front wheel, with dangerous results.
If you do want a front-fitting seat, Dutch company Bobike  make ones suitable for 1-2 year olds that can be fitted with a windscreen. This greatly helps to protect against wind chill and rain.
For children aged up to four or so, the Weeride Kangaroo  is a better choice because it’s designed for a heavier passenger.
For more information on CTC's view on front child seats, read CTC Senior Technical Officer and Engineer Chris Juden's blog on front child seats. 
Riding with a child seat
Even if you’re used to riding with rear panniers, a child seat takes some getting used to. Panniers put the weight around or between the axles. Child seats put the weight above and – more significantly – behind the rear axle, which destabilises the bike. Get a plumb line to check where the base of the seat is relative to the rear axle. The shorter the distance it is behind the axle, the better the handling will be. If it’s level or in front, so much the better. There’s no hard and fast maximum distance, but keeping it under 10cm is a reasonable rule of thumb.
Before you ride with your child on the seat try loading it up with a heavy weight, such as a 7-10kg sack of potatoes, and take it for a ride. That will give you a clear idea of how different the bike will feel with a passenger on the seat. At first, you will wobble, particularly at slow speeds. Don’t be tempted to stand up on the pedals to power uphill. The bike will handle better with your weight on the saddle, so change down the gears and spin instead. If that fails, get off. It’s easier than you might think to fall when you’re going up a steep hill. (I did it twice in eight years of child seat use. The wraparound seat prevented any injury to my passenger both times, but it was still a nasty shock – and I took some nasty gouges.)
You can stabilise the unbalancing effect of a rear seat to some degree by using low-rider panniers on the front of the bike and filling them with the picnic, toddler paraphernalia or shopping. The extra weight around the front wheel will steady the steering and keep the tyre on the tarmac – especially uphill, where the lightly-loaded front end can otherwise become skittish.
Front seats don’t have such a dramatic effect on handling, but it’s still worth taking the aforementioned spin with the spuds so that you get a feel for riding the loaded bike.
Unless you have a step-through frame, you will need to practice getting on and off the bike with the child seat in place. If you swing your leg over the saddle like you’re used to doing, you’ll risk kicking your passenger in the head. Instead you need to step over the top tube.
Feet in spokes account for half of all child hospital admissions that involve child seats. Footrests are not enough; feet may slip off or your child may simply forget and let legs dangle. It’s essential that any seat has secure foot straps, ideally in wraparound foot wells. Be aware of what else might reach the spokes – items such as scarfs, mittens on strings, and long laces – and make sure they can’t. The skirt guard that’s fitted to Dutch roadsters is a useful extra barrier.
Little fingers can also get caught, usually in an adult’s sprung saddle rather than the spokes. If your saddle has springs, either swap it for one that doesn’t or make or buy a finger guard. Bobike’s Saddle Spring Protector is what you need if you don’t fancy doing some DIY using a strip of stiff plastic and some zip ties.
To keep your child secure, most seats use a three-point harness, with straps going over the shoulders and securing between the legs. A better set-up is to have a waist belt or bar as well, as toddlers can sometimes slip out of shoulder straps when asleep. Seats that tilt back alleviate this problem, because your child won’t be slumping into the straps.
Child seats aren’t as conspicuous as child trailers or trailer cycles when you’re on the road, and some drivers won’t give you such a wide berth. If that’s a problem where you ride, consider a bright ‘baby on board’ sticker or a flashing LED light fixed to the child seat.
Bicycle child seats should offer full back and head support. Even then, a sleeping child’s neck won’t be well supported so it’s best if the seat also reclines. If it does, you can also use an inflatable, horseshoe-shaped neck pillow (from baby shops, and intended for use in car seats) for even better support.
Some kind of seat padding is essential, and it should be readily removable so you can wash it. Recently potty-trained kids will wet themselves at some point, usually when you forget to bring spare pants and trousers! For greater comfort, use fatter tyres on your bike and run them at a slightly lower pressure; the bigger air pocket in the tyres will ‘eat’ bumps and absorb vibration better.
Off-road, stick to smooth tracks to prevent bouncing your child around. Save mountain biking proper until your child is old enough for his or her own bike, or at least the back of a tandem. A fall off-road at an early age could deter your child from cycling even if it doesn’t result in serious injury, while shaken baby syndrome is a risk for infants forced to endure choppy singletrack. A youngster in a child seat can’t move around to absorb impacts like you and so will feel every jolt. It’s common sense, really.
Weather protection is also essential. Children on child seats get cold very easily as they’re not generating heat like the person doing the cycling. Put at least one extra layer on your child than on you – fleece-lined all-in-one outdoor romper suits are good, as are salopettes in winter.
When cycling in Britain you’ll also need rain protection. Soggy kids can get chilled quickly. You could adapt a buggy rain cover or a canoe spray deck, or you can buy a dedicated child seat cape from Edinburgh Bicycle Co-op (£15, www.edinburghbicycle.com ). This will help keep the wind off as well as the rain.
In summer, children in seats burn easily – especially on the back of the neck if they slump forward. Use plenty of high factor barrier cream. On sunnier days you might even want to fit a cap under their helmet – a traditional cotton cycling cap for adults fits surprisingly well.
Flies and wasps can freak out small children, who often attract them by being sticky. Take wet wipes on any ride that will involve eating or use some kind of repellent.
Small-wheeled folding bikes tend to handle poorly when fitted with a child seat, even where this is possible (usually by fitting a cantilevered seat).
Recumbent cycles don’t have the seat tube that some seats require, but any bike or trike that can be fitted with a conventional rear carrier rack can take rack-fitting seats.
Tandems can be fitted with rear child seats and are much less affected by handling issues. Upright tricycles with two wheels at the back can take two child seats between the wheels, facing forwards or back.
To use a child seat on more than one bike – on mum’s as well as dad’s, for example – buy an extra rack or bracket for the seat when you purchase it. While seats are usually quick-release, racks and brackets stay fixed to the bike because they take minutes rather than seconds to remove.
It can be tricky getting a child into and out of a child seat if you’re on your own, even with a wall to lean the bike against. Toddlers are heavy and it only takes a foot snagged in a seat strap when you’re lifting your child to send the bike crashing to the ground. The Esge Twin Leg Kickstand  looks like a motorcycle propstand and is one of the few kickstands strong enough to hold bike and child upright while you sort out buckles and straps. That said, you should never leave a child in a seat unattended. It doesn’t take much to tip over a top-heavy bicycle.
If you find it hard to balance when looking round with your passenger on board, then it’s a good idea to fit a handlebar mirror such as the Busch und Müller CycleStar . Not only will you be able to monitor traffic behind you, you’ll also be able to see if your child has fallen asleep.
Some child seats come with an integral reflector on the back, but few have mounting points for lights, which you must use if you’re riding after dusk. As a seat post light will be obscured by the seat, your best bet is to mount a light on the back of the carrier rack.
If you’re planning to walk with your child at the end of your ride, the Steco Buggy Mee Deluxe  is a great help (it’s Dutch but can be ordered direct). It’s an adapter for the rear rack that enables it to carry a folded-up pushchair. It fits to one side of the bike and projects backwards, and so won’t interfere with your rear-fitting child seat.
Information from this guide is taken from The CTC Guide to Family Cycling.