Shopping Advice (scroll down past the advice to the products if you like)
Overview - You can carry your child on the back of your bike from when they're about one year old until they weight about 20kg.
Maximum Passenger Weight - All the seats we've come across regardless of strength and quality, recommend a maximum of 20 to 22 kg for the passenger. This maximum is set not by the size or strength of the seat but because it gets difficult to handle the bike safely with a heavier passenger moving about on the back.
Rack Mounted Seats - The rack can be left on the bike and the seat can be attached or detached without tools in about 30 seconds. The racks are basically the same design as most quality luggage racks, and so can be used for carrying luggage on directly or for hanging panniers from.
Seat Tube Bracket Mounted Seats - These attach to a bracket on the seat tube of the frame, via a swing arm which allows for a bit of suspension. The bracket will not suit all bikes, however, due either to frame size restrictions or gear cables in the way.
Harnesses - Some are more effective than others. All we've seen have straps coming over each shoulder to hold the child's torso back in the seat. But they can either re attach to the back of the seat around the stomach, effectively stopping a sleeping child from sliding too far forward on the seat or attach to the base of the seat between the legs. The disadvantage of this is that it is possible for a small child to slide quite a long way forward on the seat if they're sleeping of just lolling about. We suggest remedying this at home by adding another harness strap around the child's waist and tied behind the back of the seat - a strap will be kept in place between the back and the base of the seat.
Head Rests - Some seats have them and some do not. A seat with a higher back or headrest will make it less likely for the child's head (helmeted head) to contact the ground if you drop the bike, and will make sleeping more comfortable. The downside can be that the child's helmet can bump on the back of the seat a lot while you ride.
Foot Retention and Spoke Guards - You don't want your child to be able to put their foot into the turning bike wheel. Most seats have straps to retain the passenger's feet, some have adjustable foot rests also, so that a small child's feet are not left dangling. Becoming less common now is the separate plastic shield to be fitted between the seat and the rear wheel. Though effective, these were difficult and fiddly to fit, but can be worthwhile if there's a possibility of your child's feet reaching the spokes of the wheel.
Sprung Saddles - BEWARE!!! If your bike has a saddle with traditional coil springs, you MUST cover these springs so the child cannot insert their fingers into the springs. You don't want your child's fingers in the springs when you go over a bump.
Colour - They can be hard to find, but a yellow, orange or white seat will be easier to see in traffic. However, most child seats available for purchase in Australia are grey.
Removability - Most seats are quickly and easily removed and reattached to the bike so you don't have to leave them on all the time.
Hand Protection - Look for hand rests that are set in from the edge of the rest of the seat so that if you drop the bike and your child's hands are on the hand rests, their fingers are less likely to be caught between the seat and the ground.