Hold off on riding with babies under 1 year old, says the U.S. Consumer Product Safety Commission. (Some states have laws against it.) That’s because your baby doesn’t have the neck strength to control head movement in a sudden stop and can’t support a helmet. But once she’s old enough, choose a seat based on your comfort level on a bike. A child seat on the back of a bike is more visible than a trailer, but a trailer is easier for less experienced cyclists, says Charlie Short, program manager for the City of Chicago’s Bicycling Ambassadors, a bike education and safety program.