M M Cyclery

The primary determinant of when an infant can join his or her parents on bike rides is the strength of the the child's neck.  Because of the jostling and the additional weight of a helmet (8-10 oz.). 

Usually by age 12 months parents can start checking with the child's physician to see if they have the neck development to safely go for a bike ride.  Most toddlers' neck and shoulder muscles can tolerate the weight of a helmet and absorb shock from bumps in the road at 1 years old.

There are no studies on the best method to carry an infant on a bike.  Here are some factors to consider:

Child seats / Baby Carriers

Physics tells us that a child, in a child seat, mounted on a bike, raise the center of gravity of the bike.  This changes how the bike handles and create instability.  The heavier the child the greater the impact.  But, the weight of an infant is negligible compared to the size and strength of most adults so usually the change in balance is not unacceptable.  If you want to practice before you put you kid into the child seat, load a book back with the appropriate weight of books and strap it into the seat and take it for a ride.

Kid seats tend to work well for children 1-3 years old.   There is anecdotal evidence of children of 33-44 lbs., being carried in child seats.  In fact kids usually get too long for child seats before they get too heavy.  

For all users the most difficult aspect of child seats is usually getting the child into and out of the seat.  One danger of bike seats is not when the bike is being pedaled, but when it is stopped. When the rider gets off the saddle, or dismounts, it may be difficult to maintain the bike's balance and keep it upright.  This is when some accidents occur.  Small adults generally have the most trouble loading and unloading the child.  If the parent can manage this usually they are able to ride with a child seats safely.

In the case of a crash, with child seats, even a good one with heaps of safety features, the child is likely to suffer at least minor arm and neck injuries. With poorly designed rear mounted bike seats, there is also some danger of the child's foot getting caught in the spokes.  In the USA, kid seats should meet the ASTM 1625-00 safety standard.

Child seats certainly have the advantage, especially in an urban area, of not adding to the size of the "foot print" of the bike, which may lessen harassment by motorists.

Child bike trailers

Trailers are more stable and affect the handling of the bike much less that bike seats.. Trailers with chain stay (rear triangle) hitches affect bike handling less than trailers with seat post hitches. Trailers also have the advantage of being able to carry larger children (1-4 years) and multiple children. (several trailers are rated to 100 lbs.)  Kids can be set-in the trailer with toys, books, drink, food and other amusements. The fact that the child is surrounded by so much entertainment and can nap in comfort in their royal coach, they accommodate longer rides.  Trailers can provide more weather protection -- rain and sun . Sitting low, with a low center of gravity, falls are rare and short.  The typical brightly colored fabric used on trailers is very visible to motorists.  The down side is that the child sit low and has a restricted view. And, trailer have a larger foot-print, which may be a problem on narrow roads and in congested urban areas -- instead of sharing a lane, you are more likely to have to take-up a lane for safety.  But, rather than inciting harassment, trailers more often seem to generate friendly curiosity. The best trailers have the added safety features of a five-point harness and roll-bar. Face forward designs allow easier communication between the cyclist and the child, than rear facing designs.   The child is also easier to monitored with the use of a handlebar bar-end mounted rear view mirror.