My theory - no harm, no foul Sounds like she had a great time bouncing with the other kids, and you were right there if something did go wrong. Letting go is hard when they look so little next to a bunch of bigger kids, but it's actually good for them - challenges them to stretch their limits and try new things. I'd definitely try talking to your DH about why he thought it wasn't ok, in a situation where you're not right there as it's happening - chances are he has learnt from the experience and only lashed out a bit because he was fretting about your DD.

My own DD is 9 now, and absolutely LOVES hanging out with her littler cousins, helping them on the play equipment and so on. It's a win/win as a lot of older kids are like this with littler ones too