Making vanilla extract is one of the easiest kitchen DIYs. It is a great, quick afternoon project. I don't know if it's kid-friendly but that's up to you.
Slice all of your vanilla beans in half lengthwise. Do this slowly so that you don’t cut yourself. Then cut all your halved vanilla beans in half width-wise.
Place 8 vanilla bean pieces in each bottle. Remember that you cut your beans up, so this equals 2 beans per bottle.
Fill each bottle with enough vodka (or other liquor if you are going the exotic route) so that the tops of each vanilla bean piece is covered.
Close each bottle and store in a cool, dark place for 8 weeks. Each week shake the bottles once or twice.