depends on what you want the parents to do!!! (by parents, I mean any adult that they bring with them, uncle, grandma etc!)
You could do what you usually do - circle, game, activity, drink, game, circle, if that is what you normally do, but just pick your games carefully!!! something where they compete (slightly) against the adults would be fun for the rainbows, but not too taxing for the adults. I would let the adults know that it will be a rainbow meeting with them taking part, not just watching. Maybe have some extra leaders (or their parents!) on hand for anyone who can't stay with their daughter, they can 'borrow' a parent for the night.
We have had a few Parents Nights over the years. For some of our Promise Parties where the girls had requested activities with parents we did a few silly sing-along/dance/action songs that the parents joined in which was fun.
We have also done a few as sponsored events, where the girls and the parents got sponsored. One was a dance-a-thon and another was Rainbow Olympics (a bit like a school sports day) where we had Rainbow races and parents races. The dads were very competitive!
We've done loads of these and they always go down well. Our favourite was silly sports. I typed up the instructions and put out equipment and families moved round to any station that was free. Make sure to give a little welcome talk with lots of explanation and say thank you for coming at the end.
The Rainbows love it if they practise an action song for a few weeks beforehand and get good at it so they can laugh at the embarrassed amateurs trying to join in for the first time!