There are large water slides, a "lazy river" and a separate pool to float around in.
Coco Key Water Resort is an indoor water park located adjacent to a hotel. You can visit for the day, or plan an overnight stay. Although somewhat on the higher end of an entrance fee for the Fitchburg area, it is worth the money to at least experience this park one time. Who knows, you may love it and want to buy a year round pass!
There are plenty of areas to sit and relax while the children swim and/or frollick in the splash playground structure. Kids can wear life vests that are free to use, or not if they are comfortable enough with swimming and water. The place itself is kept clean and relatively comfortable for families. Be aware that it is humid inside, so dress lightly, and don't be afraid to get wet.
There are bathrooms, changing areas, tables, chairs, loungechairs, and walking paths around the whole indoor arena. Plenty of lifeguards patrol the pools and playgrounds, so you can feel rest assured they are looking out for everyone's safety.
You can bring your own food/snacks and drinks, or you can take advantage of the food vendors they have there. (Pizza Hut...) There is also a small arcade with video games and skeeball that you have to pass through on your way to the water park, so be aware that your children might want to play these too. You can purchase tokens from the attendant. The kids earn tickets and can cash them in for prizes like Chuck E Cheese.
If you don't like crowds, plan your visits around vacations and school breaks. It can get quite busy when the kids in the area aren't in school! Otherwise, have a great time!