Hi Siedah,
Let me be one of the first to say "Welcome home!" to Disney Vacation Club!
There are areas created just for very young children at each of Walt Disney World's water parks. At
Disney's Typhoon Lagoon, little ones can enjoy splashing in the Ketchakiddie Creek area, complete with pint-sized slides and water features. At
Disney's Blizzard Beach, young children can have fun in Tike's Peak, again with smaller slides and water features. At both parks, children must be 48 inches or under to play in these child-sized areas. Both of these areas are adorable and young children have a lot of fun at them. Also, children under 3 years old do not need a ticket, you your two littlest children would be free.
However, I do think that your 6-year-old might tire of these smaller kid areas, and might want to explore other parts of the water park. So you have to consider if you are willing to split up your traveling party a bit for one adult to stay with the littlest ones while another explores the rest of the park with your 6-year-old. There are some attractions, such as the wave pools or lazy rivers, that you can all enjoy together.
I am not sure which Disney Vacation Club resort you are staying at. The Disney Vacation Club resorts have amazing pools, containing waterslides and fun water features. It is entirely possible that your children will be more than happy with these pools. I would suggest going to the pool at your resort first and seeing if your children are happy there, and deciding from there if you would like a bigger water experience at a Disney water park.
I hope that this information helps you with your decision, Siedah! Please do not hesitate to ask if you have any further questions.