Have them sort change, and eventually to count it. It teaches them to gather things that are alike, it's an introduction to money and it occupies them for 15 minutes! Just make sure they're old enough to be past the point of putting coins in their mouth.
A wise friend once told me that the kids will do as well as you do. You can’t be a good parent if you’re a miserable person.
Do what you need to do to stay healthy and sane.
There are always blessings hidden within heartbreak: a friend you would never have met otherwise, an opportunity that would never have come up, an experience, an encounter, a promotion, etc. Always look for the blessings.
Discuss the concept that “It’s not always about you.” Some days need to be about supporting someone else in their joy - or sorrow. Your needs take a backseat.
Your life is way bigger than one relationship. Or one grade, or one job, or one choice, or one event, or one gift. Make room for all of it even when some of it will most certainly hurt.