I have not been there, but judging on reviews I've read, I think it's a pretty safe bet to call T-Rex a Rainforest Cafe with another theme.
Here's the menu on T-Rex. I personally wouldn't spend money on a meal here. Basically, I think it's too expensive for the quality (though it's probably large quantity if judging by the Rainforest Cafe which I have been to.)
T-Rex Menu Downtown Disney Walt Disney World
If you look at the entrees on the T-Rex menu compared to Raglan Road, Raglan Road actually comes out to be less expensive:
Raglan Road Irish Pub Dinner Menu - Pleasure Island - Downtown Disney
Considering you have older girls (and not kids under 9...) I think they might like Raglan Road better than T-Rex and I'll suggest you take a look at that instead!
ETA: Raglan Road is also one of my favorite restaurants on property. Eaten there twice now and have had a fantastic meal and a fantastic time both times!