The correct option is B we / they
The subject pronouns are I, we, you, he, she, it, and they.If your pronoun is doing the action, you should use a subject pronoun. In the first case, the speaker(s) are doing the action of not taking the children, hence, the subject pronoun in first plural plural is "we". In the second blank, the children are at school, therefore third person subject pronoun in plural must be used, which is, "they". Hence, Option B is correct. The rest of the options do not adhere to this rule, hence incorrect.