Yep, they're ponies!
Those are the short-legged pit ponies, descendants of the poor things that used to spend their lives in tunnels underground back in the days when there was still tin mining on Dartmoor.
But they're no bigger than the big breeds of dog, and it's always funny to watch them coming eye-to-eye with something like a great dane and trying to figure out what species each other are. The dogs are never quite sure whether to eat the ponies or mate with them, and I've seen them trying to do both.