I'm not sure how old your kids are, but we have a children's science museum right in downtown Fort Lauderdale that would be a very short drive from the Marriott where you're staying. Their website is
www.mods.org and there are things for a variety of ages. Some of it is hands-on, some is geared towards little ones, and some is more scientific and for older kids. There's also an IMAX movie theater there. I think their website should tell you what movies are playing currently and maybe will tell you about current exhibits but I'm not sure.
Even though I've lived in Fort Lauderdale my whole life, I've never been down to Seaquarium, so I can't help you with that, although I do personally think it's a bit on the expensive side (considering what I hear they have to offer). The Miami Metrozoo is less expensive than Seaquarium, but then again, you can go to a zoo anywhere - Seaquarium is much less common.
On a Disney note, don't forget that there's a Character Outlet (like they have in the outlet malls in Orlando) in Sawgrass Mills mall, which is about 30 minutes west of your hotel.
There is a county park that has a water playground area. They used to have water slides, but they may have gotten rid of them. I see on their website that they have a cable-pulled water skiing thing.....might be something that an older child would like to be able to say they'd tried. I believe the park has free admission during the week, but it does say the water playground has fees. I'd be happy to call and get prices for that and the water skiing if either one interests you. I know they're still outdoor and wet activities, but they're at least different than the beach.
On a totally different note, there's also a children's art museum that would be about 20 minutes away from your hotel. It's called Young At Art and their website is
http://www.youngatartmuseum.org/. I haven't been there in a couple of years, but my son went about a year ago when he was 6 and he loved it.
I'll keep thinking about other things. How old are your kids? That may help me think of things.
By the way, in Beach Place itself there is a Howl at the Moon. If you've never been, it's a singalong piano bar (like JellyRolls at WDW) and it's soooooo much fun. I don't know if you'd be able to get a sitter or not, but it's a fun night out if you can.
We went down a few times with the kids. There was always LOTS to do! (she planned something for every day!). The Seaquarium, while being no Sea World is worth a days trip. Also, there is Lion Country Safari not too far away, Parrot Jungle was not all that great. Just a suggestion....when we were heading down her way, she made it CLEAR to us to be sure to stay EAST of 95! 
Don't know what is west of 95 but she did suggest us NOT getting out of the car to use a payphone if we got lost!!!!! 
Some of the animals like the Bengal Tiger and White Tiger were impressive.
Got some good shots of that too. There is the Koala Bear exhibit, I expected that to be better than what it is. There is a lot of walking to do, not many places where to eat and it's a LONG drive South. Personally, I don't plan on going back soon.
and the kids will love the glass bottom pool.
The NEW Parrot Jungle is OK, they just need to put a few rides there, to make it better.
There is also the Dania Beach Rollercoaster in Dania off the expressway, and yes it is EAST not West.
It also has a go cart and video game place too.
I have heard a lot about it and drive past it whenever I take Sawgrass E-way to connect with I-95. It would probably take me about 20 minutes to get there from my house, via Sawgrass. I'll have to check it out soon. 
