Our children all learnt to ride on a little Dawes bike 12" wheel which cost ?50 in 2008. It's been passed on to friends and is still going strong. I think spending a lot of money on a kid's bike is a choice not a necessity. As long as it has proper wheels, not plastic, and tyres, it'll be good enough. We bought our eldest son a ridgeback when he was 8 and it lasted for 4 years. Now passed to younger son. If your son loves riding a bike he will learn on anything. I know too many people whose kids just don't have any interest in riding bikes and have expensive frogs and isla's sitting unused in their hallways. Check out Herne Hill Velodrome beginner classes if you want your son to try a proper bike - i think they have frogs.