What is the best minicross for a child of 4 years?

Answer 1

A 50cc automatic with training wheels.

Yamaha PW50
Fully automatic, no shifting - drive shaft, minimal maintenance
http://www.yamaha-motor.com/sport/products/lifestylehome/home.aspx
Go to - Off-Road Motorcycle

Suzuki DR-Z70
Electric start - 3 speed automatic clutch (if he's too young to understand, just put it in 1st for him/her), he won't get bored of the power as he grows into it.
http://www.globalsuzuki.com/motorcycle/index.html
Go to - Offroad

Honda CRF50F
3 speed automatic.
http://powersports.honda.com/motorcycles/index.asp?bhcp=1
Go to - Off-Road

They all have throttle stops to keep from going to fast.
You can adjust them to walking speed.
The Yamaha is ideal for a pre-schooler (no shifting)
The Suzuki is nice with the electric start and he won't outgrow it.
When you get to each site - check out the Features of each.

Training wheels
http://www.powersportrider.com/CGI-BIN/ZCATJPG?catalog=ST0206C
Pick - Offroad Catalog
Go to - Index - Training Wheels
Look at the kid on the Yamaha!

Some additional reading for parents of children riders.
http://www.amadirectlink.com/amrace/torace.asp
Go to - Getting kids started right & What kids get from riding

Answer 2

Yamaha pw50 or a Honda xr50 with training wheels