Here are a couple of things that we have done. First, we had a "Make a Deal" night. This required a lot of preparation on the part of the PTO, but it was well worth it. We had one of the male teachers dressed in a tux, on stage with 3 large boxes, wrapped, and turned upside down on tables. The "host" would ask for various items from the Mom's purses (just like Monty Hall used to do). The first daughter to get to him at the stage with that item got to choose box 1, 2, or 3. The "hostess" on stage stayed behind the boxes and replaces prizes as they were chosen. The PTO purchased some prizes, but we had some really great prizes donated from businesses around town. Things like flower arraingements, restaurant gift certificates, movie tickets, beauty salon certificates, even a weekend at a local bed and breakfast. Everyone had a great time that evening. None of the mothers knew about this what we were doing, so they couldn't bring extra things in their purse to cheat.
Another time we had a line dancing evening. Everything was decorated in western decor and we asked the Moms and daughters to dress for the occasion (jeans, western scarves, etc.) We had a couple of the teachers that do line dancing up on stage teaching line dancing to anyone that wanted to participate on the "dance floor" below. It was a fun evening for all and didn't take a lot of work from the PTO to set it up.
Good luck!