Well, I read somewhere that bullfrog tadpoles take two or more years to develop into frogs.
As for the legs, I don't know that the frogs can remain tadpoles for the rest of their lives. What temp is the water? How deep is it? Does the tank have anything like a lily pad in it? Now that I read the site, I may end up putting a paper plate into my tank. I've also found out that the tadpoles do learn how to eat algea discs. You may try spinach and frozen (not freeze dried) bloodworms for protein. And raising the temp may help, but I wouldn't get it too hot because it would increase the respiration of the tadpoles. And I would have a filter in the tank, if it doesn't already. The ammonia can build up very easily in any size tank and would require 100% water changes to keep the tads from coming down sick or dying.
Also the reason that I dislike freeze dried food is that it is known to give aquatic frogs and fish constipation, even to the point of death. So I steer away from it, but I find that my African Clawed Frogs love the frozen food and won't touch anything else.
I also heard of Frog and Tadpole bites, but I have fed them to my two bullfrog tads and I have never seen them eat them, but there is no reminent of them on the bottom of the tank.
I hope this helps. I'm a newbie too and I just looked up how to care for my own two tads and the fact that it takes so long for them to grow was a little of a shock to me.