Learning to ride a bike can be a frustrating business. Children who lack confidence in movement, or who have poor balance are often afraid to attempt this activity. Some children may manage with stabilizers removed yet want to keep up with their peer group.
When you your child feels ready to move onto their bike, make sessions relaxed with no pressure. It is useful to break learning to ride a bike into stages to make it less scary. The idea is that the child gains confidence at each stage.