Yah, if I had any kids, they'd never have tasted a meal without onions in it.

Dice one medium onion, and fry in butter. While it's frying, check the rest of the recipe. If it turns out it doesn't call for an onion...it'd better be dessert. If that's the case, eat the onion while preparing the dessert.

(Many recipes then continue "dice 5 more medium onions" around me :-)).