My son Lance who was 4 in June rode his bike for the first time without Stabilizers!!!! I promised him a new bike if he could. He just got on said push me daddy and he was off! he had a bit of trouble turning but got the hang of it in the end! So now need to decide if we go for an 18" bike or get the isla bike with 20" wheels as he just falls into the height for this. Anyone with any experience of this size bike?