Took my two littluns to their first BMX race meet a couple of months ago at the Patchway track, Bristol. The youngest competing was 3 1/2, the oldest 42. There was a good all-welcoming family vibe, but the club secretary I'd befriended a few weeks prior wasn't about to let ike; 3 3/4, out on his pink plastic wheeled, white solid 12" foam tyres hand-me-down (or his German runner-bike he's much faster on). Nor Pippa on her 10kg pink fairy princes Tescos bike. The super light Redline Micro junior racing BMX (with 20" skiny wheels) I bought for her on eBay turned up 30 minutes before the start of the first race so that was just as ridiculous a proposition.
Fast forward several months, and P is sort of getting the hang of the very high crank. Ike is now on the Tescos heavyweight, but flying. His 4th birthday is approaching and I decided he deserves an up-grade and a break from his sisters hand-me-downs. Micro-Mini BMXs (with 18" wheels) are hard to come by second hand, and to be fair I think he's still a bit too wee for the racing.
Struck lucky on Gumtree with this mint Islabikes Cnoc 16". It's a beautifully made aluminium framed bike (only 7.5kg), and it looks like it's only ever been used in-doors. I've taken off the mudguards, front brake, and cut 5cm off the width of the bars.