Today one of my clients brought her 3 children with her, they're between 5 and 8. We got out the kettlebells and did swings followed by a run across the stadium and back, rows and run, etc. The kids ran with us.
When she did inverted rows on the rings, one of her daughters was very impressed. On the next set, she said, "The same again, mum, that's boring! Do a backflip!"
All we needed was the dad and I would have had the whole family there. This is something they never told me about in PT school.