We've all been there.
In the middle of a brilliant family day out, junior doesn't make it to the bathroom in time or baby needs a new nappy and you forgot to bring your changing bag.
All you can do is head home early with a very disappointed family!
However, some parents in America are starting to help each other by leaving spare pants, wipes and nappies in baby changing rooms.
One woman found a package in a local store this week.
What a fantastic idea.
I hope it catches on...