Hi Kimberley!
There are tons of fun things to do at both water parks for smaller children. My son is 3 and about 41" and absolutely loves splashing around. There are several attractions that he is not tall enough for, but there are still plenty of attractions that will fill up your day.
Check out the
attractions website for Walt Disney World. On the left, you can filter by height requirement. You'll find that there are lots of fun things for your little ones to do at both Typhoon Lagoon and Blizzard beach.
My son loves the
Toboggan Racers at Blizzard Beach. He especially loves that he can race Mommy and Daddy down to the bottom. Both parks have a family raft ride that both of your kiddos can ride with you!
Tike's Peak and
Ketchakiddee Creek are designed for smaller kids in mind with splasher areas and small slides.
The Surf Pool at Typhoon Lagoon is always a great time and there's a slide right next to it that both of your kids can enjoy. How about a ride in the lazy river? Both parks have their own version where you can relax the day away.
I bet your 5 year old would love
Ski Patrol Training Camp where they can test themselves on the iceberg bridge. There are tube slides right next door for both kids.
As a water park veteran, I can assure you that you can find a whole day's activities at either Typhoon Lagoon or Blizzard Beach.
Have a magical day!
Leslie