We just got back from spending 2 days at St Pete Beach after spending a week visiting grandma in Spring Hill and 5 days in Orlando.
You didn't say how old your kids were, but we stayed at the Alden Beach Resort at St Pete Beach. It's right on the gulf, the beach is really very pretty. The hotel is reasonable priced -- check out their website. It's very clean, a little old, but certainly not outdated. They have 2 swimming pools, a playground area for little kids, beach volleyball for bigger kids. We stayed in a Lanai suite which had a private balcony overlooking the gulf. It had a living/dining area with a sofa sleeper (right by the balcony, then a very small kitchenette, a nice size bathroom, and then a bedroom with 2 queen beds. Oh, they also had 2 lighted tennis courts, shuffleboard, ping pong, game room, a large patio area with gas grills if you want to cook out.
My kids are 15 and 16 and loved it. So did I!