Its certainly an idea, but if there was an actual ice age the gang probably wouldn't surivive because of how they are all cold blooded - one of the reasons the dinosaurs even existed was because of the really warm period the earth went through in the mesozoic era.
Actually, no one really knows if they were warm-blooded or cold-blooded. But there is more evidence to support them being warm-blooded (including lots of blood vessel holes or whatever in their bones, something that, today, is only present in warm-blooded animals). Another evidence comes from Brachiosaurus I believe. In order to pump blood all the way up that neck, it would need a 4-chambered heart, something only warm-blooded animals have.
Also, if Littlefoot and his friends and the other GV dinosaurs were indeed cold-blooded, they should have died off in LBT 8, when that snowstorm hit. But they didn't; they survived and remained active, and this snow storm didn't last a short time; it lasted long enough to kill off the plants. And at one point, Mr. Thicknose was completely covered in snow, and yet was still alive when Littlefoot came across him. To be covered in snow, Mr. Thicknose had to have been laying out in the snow for a long time. If he were cold-blooded, he should have been dead by the time Littlefoot and the others found him, but he wasn't.
If anything, this proves that the LBT Dinosaurs are indeed warm-blooded.