SeaWorld is my favorite too. I think it's a great choice for a 10 and 12 year old and a place all ages can enjoy together. I also like the deal they have where you can go a second day within seven days for free, just by stopping at the customer service desk for your ticket. Or if you want to mix it up more than that and you like waterparks, I think the SeaWorld / Aquatica combo ticket is another nice option. // We can't go to Orlando without doing SeaWorld -- my whole family and extended family just love that park.
Second all this. My whole family likes SeaWorld, but the 9-13 year olds like it the most. We do the second day free deal and also get their dining deal, which is a lot more flexible than Disney's Dining Deal and perfect for my chow hounds, particularly my 13-yo ballet dancer. She loves Disney (some of the others don't), and all things being equal would rather go there, but the dining deal puts SeaWorld in first place every time.
The SeaWorld dining deal is all fast food or buffet-style stuff, though; the food is fine but not spectacular, however what the kids love is you can go through the line as many times you want (limited to 1 drink, 1 entree and 1 side or dessert each time), anytime you want (once that particular restaurant is open), and you're never too far from a participating restaurant.
SeaWorld is more about the shows than the rides, but personally, I only like two of the shows but love the aquariums and dolphin viewing areas and feeding the critters and that kinda stuff. For some reason I get a real kick out of an aquarium below me, or above me, or the tunnels through the big ones. SeaWorld is still a very different experience than, say, Ripley's Aquarium in Gatlinburg, even though both have the long tunnel.
SeaWorld is beautifully themed. Jewel of the Sea, the aquarium in the middle of the Journey to Atlantis ride is tiny, but it really does feel like being in a little jewelry box, with the fish as the gems, while the Mantis aquarium is laid out in a sweeping, flowing way that, for me, sort of mimics the rollercoaster up above.
And I love all the greenery and flowers and waterfalls. Could be SeaWorld particularly appeals to those who love the Polynesian resort.