Your kids will have a great time on the ship and the ports of call.
If you are very adventuresome, take them to Yelapa for an amzing beach day a bit south of Puerto Vallarta. This island-like beach is very rustic and seems like Gilligan's island. There are no cars so the only way in or out is by water taxi. It is an amazing beach with lots to do for kids. The little grass shack style hotel has a wonderful swimming pool made out of giant boulders attached with cement. You can use the pool if you buy lunch there. The beach there is great for swimming, parasailing, jed skiiing, hiking, etc.
The food at the hotel is great. They have wonderful avocados stuffed with shrimp, whole fish cooked in garlic, lobster, etc. You can eat on the beach under a palapa.
Just remember this is VERY rustic. But it is also something your kids will never forget.
We just got back from cruising the Mexican Riviera on the Vision with our kids aged 6, 9 and 11, but last year we went on Star Princess with no kids. I'm not sure about the Diamond, but on the Star, the kids program was housed in a really nice space with a good preteen lounge and arcade. The pools were beautiful, and the ship itself was lovely.
On the Vision, my 9 and 11 year old boys had a ball. My older son told me that it was the best vacation he'd ever had! I think they loved having the freedom to roam the ship, and the choice of so many activities. They did the children's program on some days, but not all. The 11 year old felt he was "in between" age groups, and preferred exploring on his own.
The ports were alot of fun for my kids, who had never been out of the country before. In Cabo, we went to the beach (Chileno Bay) for snorkeling, in Mazatlan we took the Colonial Villages tour for a half-day which gave them a great introduction to small towns and crafts, with plenty of time for swimming on the ship in the afternoon. In Puerto Vallarta there were tons of things to do -- jet skiing from the Malecon, hiking on jungle trails, hanging out at the beach.
Have fun! I think your kids are a great age for cruising!
We were on the Star Princess our last Mexican Riviera cruise. We have also done this trip on an R.C.I. ship and Admiral's Stardancer.
Puerto Vallarta is one of our loves. We go there at least once each year for about 2-4 weeks, sometimes longer. There is a lot to do and see there. You won't do the city justice in one day, but it will give you a little sample. Then I guarantee you'll want to go back.
Shopping is best in P.V. over the other ports. The Zona Romantica is a great areas for shopping and it is near Los Muertos beach which can be fun too. If you have any specific P.V. questions, feel free to ask. I'm not that knowledgeable about Cabo and/or Mazatlan because we have only been to those cities by cruise ship.
Francine, Having cruised on Star Princess last year, and Vision over New Year's, I agree with Chuck that the Princess Diamond would be overall nicer, but we really enjoyed Vision too. In fact, the food was better on Vision than Star. I submitted a review comparing the ships but it hasn't been posted yet. The jist of it was that we had a great time on both ships and you can't go wrong. The children's program was very nice on the Vision, and the food and entertainment were better on Vision. The ship itself, including the pools and cabins were nicer on Princess (IMHO). Because Vision is not as new as Diamond, you willl probably find a better price on RCL than on the newer ship, so I'd go with price and availability -- both cruises are lovely. jeanne