There are a few places to go with your 3 girls. The Tampa Aquarium is a great place and when they are finished inside there is a water area with slides and a pirate ship that is great fun if it is hot and they want to cool off. Make sure they wear their bathing suits underneath or there is a changing room too. (check out their website)
Also MOSI the Science Museum is another great place. They might get bored in the main museum but there is a hands-on building that they will love! And you can relax in there while they play.
Also if you like parks Lowry Park Zoo is great as well as Busch Gardens and SeaWorld. They both have waterparks across from them as well. If you go to the websites you can get tickets/packages for 1 or more parks. Right now I believe they are offering residents "pay one price - play all year" so you can go back as many times as you want until Dec. 31st.
I'm not even sure if you would have to pay for the 2 year olds at some of these places?
I also live in Spring Hill and if you don't want to go too far you can go to Pine Island - beach or Homosassa Springs Park which is about 1/2 hour North on US HWY 19.
Have FUN!