I see this is an old thread, but thought I'd give a response anyway in case newer posters have the same questions...
I'm a parent of 4 kids, and I find it difficult to get a babysitter. 4 kids is a lot for one teenaer to handle!

Plus, I get nervous having people into my house... I would LOVE it if more church youth groups, high school sports/performance groups, etc. had some type of large childcare fundraisers.
Have a "Parents night out" event one night in a large location (like a gym)...have activities set up for the kids, maybe provide pizza/juice dinner...a movie, etc. Charge a flat rate per child for the set time (like 6pm-9 pm, or whatever). You should probably check to make sure what type of local childcare laws you need to follow...I think in VA there is some laws about "drop in" type child care being ok up to 3 hours
Depending on when you need money, a fundraiser like this could also work out well during the day, like right before christmas time, so parents can have a shopping day, etc.