There are 2 species of aquatic frogs in the trade, African dwarf frogs and African clawed frogs. Clawed frogs grow quite large and will eat smallish fish. Dwarf frogs can be kept in small aquariums. But.......
It is best to keep them in a frog only tanks. Frogs find their food by smell and by the time they have found it, any fish in the tank will have eaten everything. They are almost blind, and can mistake a moving fish shape for food. Years ago I had 2 frogs with a betta and one day found the betta swimming frantically round the tank trying to dislodge the frog clamped to his tail. I separated them immediately and would never keep frogs with fish again. And then there's the problem that frogs can't tolerate fish medication so if the fish ever get sick you can't medicate the tank.
If you really want frogs, I would get another small tank just for them. There are a couple of pinned threads in the Amphibians and Aquatic Reptiles forum.