Depends on their age, of course. Check out the Bike Friday OSATA. Had it existed when my son was young, I would have bought one. Instead we bought 4 bikes for him as he grew, costing more than the OSATA which would have worked for him from kid to adult (easy to change components/gearing). Granted it is not exactly a folding bike, more like a "packing" bike. Depends on what you need.