In Emily Dickinson's poem 'I'm Nobody' the poet is speaking as a child and uses a child's voice. She makes a statement about herself - a decision she has already come to - and then asks a seemingly ingenuous question 'Who are you?' This seems to reflect the innocence of childhood.
She wants to know whether the person she is questioning is like her a 'nobody' but the philosophical nature of the question belies the childlish tone = she is making a judgement about the label 'nobody.'
'They'd banish us you know' suggests that that there is another body,society perhaps that is making those judgements and they have different values to her.
She seems critical of those people and their values, comparing them to a frog who has no other purpose than to sit croaking all day in a swamp telling everyone it's name.
She seems to be saying that you are not a somebody just because society tells you that you are - those that croak the loudest are not the ones most worth listening to in her eyes. Quiet modest people can have more wisdom and value.