"Why do you not raise this girl?"
Translation:Dlaczego nie wychowujecie tej dziewczynki?
'Dlaczego ty nie wychowujesz tamtej dziewczynki' should be accepted either, right?
No, "tamtej" is 'too far' for English "this". We understand the proximity of determiners the following way:
Polish: ten/ten/tamten (and its forms)
So clearly, 'tamtej' cannot be a translation of 'this'.
error:501 isn't "dziewczynki" girls? with an 'S' . one girl would be 'dziewczynka'.
"dziewczynki" are "girls" in Nominative (Dziewczynki są wysokie = The girls are tall) and Accusative (Widzę dziewczynki = I see the girls). But it's also Genitive singular. Most feminine words have those three forms identical.
So to understand which form is used, you have to understand what is needed. "wychowywać" (to raise) takes Accusative. It is negated here, and negated Accusative turns into Genitive (only Accusative changes case when negated, other cases stay the same). So as we need Genitive here, this means that "dziewczynki" is singular.