Children between 7 and 12 years of age should be getting a minimum of 9 hours sleep per night and aiming for 10-11 hours of sleep if possible.
A good amount of sleep helps kids to concentrate at school the next day, decreases irritability when waking up and strengthens the child's immune system (among other things).
If your child has unusual difficulty falling asleep try enrolling them in a regular exercise program e.g. swimming lessons, athletics, gymnastics.
Do not play computer games before bedtime.