Paradise Village in Riviera Nayarit, just outside Puerto Vallarta. I'm now 20 however I've gone there every other year since I was 4 and my sister was 2 My Grandparents bought a time share there, and it is the perfect place for kids. It is not a place for teenagers to run around drunk, but is geared towards families and the older crowd. There are SO many activities in and around the pool all day for the kids to participate in, virtually everything you can think of, they have. They also have a kids club if you want to dump the kids for an afternoon and have a spa day, golf day, or whatever you would like!
Depends what kind of package you can get with all inclusive, as it can sometimes be a bit pricey. However that is coming from someone who has never had all inclusive before, as we own a place there so we just go and buy grocery's at the resorts mall.
It is the perfect place to relax, and since I've virtually grown up there, it is still my favorite place to go in Mexico! Definitely look into it, you won't regret it!
Edit: Just kidding I lied...I forgot kids under a certain age are cheaper or don't even have to pay at all for all inclusive. They have a pretty good all inclusive package sale going on right now, middle right hand side of the page!
http://www.paradisevillage.com/