It varies with me. Sometimes I lie (and have used most of the ones icky posted), sometimes, if I'm feeling strong, I tell the truth and kind of dare people to deal with it. It's usually easier for all involved to lie, because people who don't do it don't usually really want to know the truth and what's behind it.
That works for adults, anyway. I don't know what to tell your kids.

sorry
Take care and stay safe.
Candy