Sarah:
When my children were the ages of yours, I preferred
Blizzard Beach over Typhoon Lagoon for several reasons. First, the children's area
Tike's Peak offered longer slides AND I could see my children for the length of the slides. At Typhoon Lagoon, the slides were shorter but there was vegetation in some places that blocked my view of my son, and as a protective mom, it just left me unsettled. I also liked all of the seating near the area along with a few picnic tables. Secondly, I found
Ski Patrol Camp fit my 5-year-old well: he was too big for the "kiddie" slides but not quite old enough--or tall enough--to ride some of the taller slides. Third, the surf pool at Typhoon Lagoon is for good swimmers. I even found myself once getting swept by the large tide, and felt the "bobbing" waves of Blizzard Beach's large pool a better fit for the skill level of my kids.
Don't get me wrong:
Typhoon Lagoon has some unique attractions in its Crush 'n' Gusher, surf pool, and especially the Shark Reef, but for younger ones, I'd go with Blizzard Beach.
Wishing y'all a magical vacation!
Whitney