The average 5 year old is on a small frame 20" bike. Look at the radius explosive, giant moda, or mongoose racer x. If he needs training wheels make sure the rear axle is long enough for them to be fitted or it will cost you more
If he doesnt need training wheels and you want gears look at the giant veer with 3 gears and back pedal brake.
If he is small then look sat a 16" like the giant animator, mongoose Mity goose or radius dinosaur these come with training wheels
If you measure his inside leg any good bike shop should be able to work out what size he needs.
This post has been edited by Luvmy4: 27/11/2012, 08:18 AM