Why do you want to freeze it is it because they are about to go off? If not it's not one that really takes a good deal of preparation so probably don't need to make it in advance and freeze you can just mash it with a fork when you need it.
AK always says not to freeze banana - think it goes black and looks a bit unattractive. As pp said banana is quick to prepare and no need to freeze. You can thin it with a little milk if it is too gloopy for your lo or if your lo is 6 months you could give it in pieces and use it as finger food.