Those look A LOT like my bullfrogs when they were at that size. However, if you're SURE you have ruled out bullfrogs, Green frogs look almost identical, they just don't get as big and they also have a lateral ridge that runs from the back of their ear alongside the body all the way to the rear leg... Looked like yours had that, so they might be green frogs.
Happy froglovin'!
Jeff
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