Came to post range bag, already been posted.
A diaper bag will shrink as your kids get older. Not that they don't need as many diapers, but you start realizing how pointless have the stuff in it is.
If I had it to do over, I'd have a go bag at the ready at all times. 3 diapers, bag of wipes, bottle with water, measured formula. Should be about the size of a half a loaf of bread. That would cover 98% of all needs. For extended trips, I would have a bug out bag. This would have a sleeve of diapers, bag of wipes, can of formula, 3 outfits and 5 bottles. That would get you through outings no problem and would about the size of a laptop bag.
Then I would consider a SHTF bag. This would include all things in the bug out bag plus Clorox wipes, change of clothes for me, $50 cash and a credit card.