When you go to the store and they pick up a candy bar you buy it immediately. You think that no one wants a candy bar handled by a grubby 2 year old.
With the second child:
When you go to the store and they pick up a candy bar and chew on it a little bit, you put it back. You think that no one will mind a little bit of chewed teeth marks in their snickers by a grubby 2 year old.
With the third child:
When you go to the store and they pick up the candy bar, chew it, slobber on it, fold it in half and generally mangle it you put it back. You think that no one will notice the candy bar shoved in the back that was destroyed by a grubby 2 year old.