If you have small children in your home, you have to be especially careful with your garage door- garage doors are the biggest, heaviest moving part of your home and can easily injure people, especially those of us with small little fingers and bad coordination.
For one thing, teach your kids to never run or play near or under the door in much the way you teach them not to run in the street- a strict, hard-and-fast rule!
Secondly, tell your kids that they may not play with the garage door opener remote. It's best to keep it out of their reach in the first place. And if your garage has one of those keypads that can be accessed from outside, you have to take extra care to teach them proper conduct. Do not ever allow them to play with the wall-button that controls the garage door. If you can, have it installed higher than they can currently reach. Hopefully, by the time they can reach it, they'll know better.
And if your kids have friends over and they plan to play outside by the garage door, make sure their friends know they're not to play with the button or play near the open door.