Welcome to the Disney Parks Moms Panel Irene!
Both Blizzard Beach & Typhoon Lagoon are amazing water parks and I don't think you can go wrong with either park. I think you'll get "Moms" that will vote for each. Both offer play areas for little ones less than 48" tall.
Ketchakiddee Creek is a water play area at Typhoon Lagoon featuring 10 different activity areas including 20 different activities with fun water features and kid-sized slides.
Tike's Peak at Blizzard Beach offers younger guests less than 48 inches tall their own watery play area with a fanciful snow-castle fountain, pop-up water jets and kid-sized slides.
Of these two, I think that Ketchakiddee Creek offers more hands on activities that you could enjoy together with your 3 year old.
Both parks feature awesome lazy rivers that your 3 year old will enjoy. Both also feature huge wave pools. A word of caution about the Surf Pool at Typhoon Lagoon - the waves are big. They come in 90 second intervals and carry a fairly strong current even along the outer edges so be sure to watch your little one. If needed, life vests are available at no charge but guests must leave driver's license or credit card as deposit.
I do have to mention that our favorite family ride is
Teamboat Springs at Blizzard Beach. My boys can't get enough of it (me either).
Please feel free to visit with all of your questions. We're hEAR to help!
Wishing you minnie magical memories :-) Allison V.