Two tips from experience:
1. Do NOT give the child drinks with sugar before or during the flight. The sugar will tend to make them even more hyper -- depending on the child. This means no fruit juice either.
2. Bring toys, but do it this way: Bring a bag with several small new cheap toys, such as cars, puzzles, etc. Bring one out once an hour or so. It will surprise the child and keep their interest -- for a while! If you only bring one favorite toy they will get tired of it soon.