Guy, yes, at least six months old, so they can sit unsupported, otherwise its bad for their backs. I have a three year old who has done about 500 miles with me, and now we have an 8month old, who I am just starting. The 7kg difference in weight makes a hell of a difference! I find hea has a tolerance of about 30mins, so longer runs have to be broken into stages, with places where he can get out and run around (and pee) for a few minutes.