One of my favorite purchases for my kids has been a balance bike, which is basically a bike without pedals. Instead of starting a kid on a pedal bike with training wheels, they learn to balance and coast first, then pedal later. My 2nd kid and first boy, Ivan, was crazy fast on a little 4-wheel toy at 20 months, so we bought him a cheap balance bike at Walmart for $35. In a few days he could roll down the driveway with his feet up. A few weeks later he was rolling around a bmx track, then the skatepark, dropping in on the biggest ramps.
He's always been a little guy, barely even making the graph for height & weight percentile. Finally when at 2 years 7 months he could touch the ground on a 12" bmx bike after cutting the seat post down. We splurged on a Specialized Hotrock and within days he could pedal everywhere.
Now Max, kid #3 and 2 years 8 months, is on a balance bike and getting closer to inheriting the little Hotrock. We had a nice sunny 65 degree day and hit the ramps today. Ivan has moved up to a 16" Hotrock we found at a garage sale. Watching them tear it up at the park is one of my greatest joys as a parent.