I was confused on the first real bike to buy my daughter when she turned four. The market is saturated with low quality steel framed department store bikes. While higher end bike shops don't carry a quality lightweight option for smaller kids.

I have owned numerous bicycles over the years: road, mountain, touring, folding, recumbent, commuter, but I never rode BMX. I have spent my entire adult life in the bicycle industry, and I pride myself in my bicycle knowledge. However I had no idea what to do for my kids.  After tons of research I learned of BMX micro-mini bicycles, they are super low to the ground, super lightweight, and cheap ( $300-$500 ).

These bicycles are setup to be super lightweight with the following features:

1. Short frames with minimal reach for small kids.
2. One speed with a solid gear for kids.
3. Only a rear brake
4. Super thin 1" tires are doubly important. Removing rotating weight makes the bike feel much lighter to ride than removing non-rotating weight.
5. Comfortable and super light plastic saddle.
6. Low spoke count rims

Micro-mini's are a no brainer for kids in the 4-6 age range. For kids in the 6-8 range look at BMX mini bikes that are slightly bigger ( seat tube height ), and longer ( top tube length ) to accommodate for bigger kids.