Good question. And it really depends on the kids.
My oldest was not quite three when he started riding his pedal bike. He was never able to figure out how to use the coaster brake. And with just one front hand brake on his 12" bike, it got quite dangerous when he would get going downhill fast. He wiped out onto his face at least once, and had a few close calls. He adapted to gears no problem, even tho it was gripshift.
My youngest never rode with a coaster brake. Went from the Strider of a 16" Ramones with hand brakes. I think he caught on fairly fast. The only thing is, he relied on the front brake much more than I realized (those v-brakes actually had brake-force "reducers" on them, sort of like a little spring that eases the bite of the pads on the rim so they don't lock up the front wheel). When he switched to his 20" bike with disc brakes, he learned fairly quickly not to grab a fistful of front brake. We were going down a big hill (it's a bunny hill for beginner skiers, but on a bike, it turns out that's pretty damn steep!) and he started really picking up speed. So I yelled at him to use his brakes. He basically just grabbed his front brake as hard as he could and pretty much launched himself to kingdom come. I watched in horror as he flew up a good 4' and belly flopped on to the grass. No harm no foul, kids are friggin made of rubber. For the most part he's pretty good now, but when we're trail riding I usually remind him at the start of the ride to use both brakes, and not rely too much on the front one, especially going downhill.
With the gears, he had a bit more of a hard time. He wasn't strong enough to turn the gripshift so I got him an entry level thumb shifter from SRAM (x3 maybe?). I pretty much had to ride behind him and tell him which button to click and which number to be on. I think the issue is kids quickly figure out that the "fastest" gear is 1, but don't realize there is an "optimal" gear depending on the terrain. So they always try to revert to 1 to "go fast"... Reading the terrain can take quite a while for some kids. It wasn't until this fall that he has figured it out on his own, and this is his second full season on the bike.
haha! same here! Eventually, I was able to convince her we'd be able to recoup a majority of cost when it came time to sell them again. As I mentioned previously, I have a buddy who bought a used one for $400 (canuckistani pesos). But I think she's still dubious. Now that my older son seems to like riding, I tried to sell her on the notion of getting him a Process 134 (a buddy was selling his kids'), but $2000 for a *used* bike was too much to swallow... Plus, he was acting like a dickhead, so I couldn't bring myself to drop the cash at that time. There will be other opportunities I'm sure.
Just for giggles, when I was looking through my pics to see when I got the bike, I found this photo from the first time he got to ride it. No front teeth, haha!
