What is the correct replacement for a 'band' of frogs?
"army", from this very interesting page.
I'm not sure at what point it was decided that every animal should have its own collective noun, but it's always seemed like total nonsense, to me. There's nothing wrong with "a group of frogs" and, since "band" doesn't necessarily mean a musical group, "a band of frogs" is fine, too: indeed, it sounds rather nice as one can imagine the musical sense, too, with the frogs croaking melodiously.
The "correct" term is "an army of frogs". However, I strongly recommend against using that because it's likely to be actively misleading. Anybody who doesn't know that "army" is the collective noun for frogs (and that's almost everybody, trust me) will assume that you're talking about a very large number of aggressive frogs.
The term you are looking for is "collective noun", a term that refers to the (sometimes whimsical) names for a group of animals, such as a murder of crows, an ambush of tigers, a charm of goldfinches, a smack of jellyfish, a pod of whales, a mob of kangaroos, or an army of frogs.
If you search on Google for
collective nouns frogs, you will find your answer.
That all said, you can use band of frogs, if you like. Words like band, group, gathering, troop, and bevy are not "wrong," irrespective of the animals being referred to. English may have a special word associated with an animal, and perhaps this would be the preferred word among zoologists. However, if you were writing a children's book, for example, nothing forbids you from referring to an ensemble of frogs, if that's what you want to call them.