Now while his body movements might have progressed at an alarming rate, unfortunately his brain still has a little catching up to do. They love trying out new tricks and stunts, but as there judgement is not yet fully developed, they end up tripping and falling for no apparent reason.
It is vital that your four year-old be supervised at all times. Your child is not aware of the dangers that are involved with certain activities, and it is up to you to make him aware of these.
You need to set limits for your child and explain in detail the dangers that are involve din certain of his activities. For instance, if your child wants to ride a bike, tell him he must wear a helmet, and explain why. Pool safety too, should be taught to your child when you are going to be in or near a pool area.