I don't remember ever having a kiddie size bike. I had a Big Wheel, maybe two, then went to a 20" BMX type thing. It was built for me by my Grandad who was a bike hoarder and had hills of parts. I remember at some point, maybe age 6, he changed out the crank for a longer one. Next I got a 24" mountain bike. I think that was at about age 10. These both got sold at yard sales. In high school I had a mountain bike with index shifters, a huge upgrade. Seem to recall this was about freshman year of high school. I gave that to a college girlfriend one spring and we broke up over the summer. I wonder whatever became of it.
It seems to me like the usual progression is from some kind of kiddie toy, either a trike or a little thing with training wheels, to a BMX to a mountain bike. What age for each upgrade? I still see 24" mountain bikes sometimes but they don't seem too common.
Also - there is a recent trend for kiddie bikes which have no pedals but no training wheels either. The idea being that you get them learning to balance from the start. Has anyone tried this with his/her kid? Did it work? Why not a scooter? Or since they are often $50+, why not just take the pedals off a MUCH CHEAPER Walmart kiddie bike?
Does any normal kid really want a nerdy contraption like this one?