When your friends come back talk to them about taking your kids? If you're going to watch their daughter they should be willing to watch your kids.

If you have a friend you haven't seen in a while you could use that opportunity to see them. Or see if husband wouldn't mind you visiting during their business trip? Or even a 3 day movie marathon by yourself where the only time you move is to eat and shower? Don't feel guilty for needing time to yourself.

You could even talk to them about scheduling date nights where once a month you guys watch one another's kids while one married couple gets to spend time alone. I'm fairly certain my parents did this with my sister and I when we'd go to her friends house overnight.