We went to Blizzard Beach last June with 3 kids, 8, 4, and 22 months, and had a great time. I originally picked Blizzard Beach because I thought the Jr. Ski Patrol area sounded like it would be nice for my just turned 8 year old who isn't overly adventurous, but he started and just kept going on all but the very steepest water slide. (Go figure!) The two younger ones had a great time on Tikes Peak.....they kind of liked the Lazy River but the 4 year old was freaking out with concern about having to go under the sporadic waterfalls and not trusting that we'd steer her around those, so I can't say it was as enjoyable as it could have been!
I'd take advantage of the fact that they let you bring coolers in and bring plenty of juice boxes, some sandwiches, snacks, etc. It's a nice change of pace from the Disney Counter service and a real money saver. I'd also highly recommend water shoes for the entire family (the side walks can be very hot) and your own towels if you really want to be able to dry off. I think rental towels are available, but it's another thing to stand in line for and they're small.
Have fun!