One-day water park admissions are certainly available you can purchase them at any Walt Disney World ticket window.
In June, both water parks will be open - so you'll have to choose which to visit. My family slightly prefers
Blizzard Beach over Typhoon Lagoon. My children like the variety of different types of slides available there. You don't say how old/tall your son is, but if he's a tween, he's going to want to explore the Ski Patrol Training Camp with its just-the-right-size activities for the 8 to 12 set. We also LOVE the fresh made mini-donuts at the Blizzard Beach donut stand.
Typhoon Lagoon has the Shark Reef attraction where you can take a swim with tropical creature, including harmless sharks. There is also a water roller coaster here which appeals more to some who don't like the GIANT slides.
Whichever water park you choose, be sure to get there early. I would plan to be at the park about half an hour before it opens. This will give you a chance to grab a chair and work in a few of the more popular attractions before the lines get long. You'll also want to have something on your feet that you can wear on the slides. The pavement at the water parks can get quite hot.
I have a feeling that once you tell your husband and daughter about the great time you had at the water parks, they're going to want to join you next time.