Toddlers can begin both wearing helmets and traveling on a bicycle at approximately age one. Before then, they may not have the neck strength necessary for supporting the weight of a helmet on top of their heads.
Helmets are made in all sizes, colors, and themes and are easily found in bicycle shops, major retailers, and online. When shopping for a helmet, check that it is labeled certified by the Consumer Product Safety Commission (CPSC). All new helmets should contain this label. A helmet for a sport such as football is a poor substitute and is NOT recommended. Likewise, buying a helmet second hand does not guarantee that the helmet is bicycle-worthy.
Most helmets will last the child for at least a year or two. Many come with removable interior pads so the helmet can grow with the child. The helmet should be worn squarely on the head and the chin strap snug so that it does not slide around on the child.