Step 1: Identify the noun to which the pronoun must refer. In this sentence, the pronoun refers to the children, which is a plural noun. Therefore, the correct pronoun must also be plural to agree in number.
Step 2: Consider the structure of the phrasal verb “pick __ up.” In such constructions, when a pronoun is used as the object, it must appear in the objective case. Additionally, since the reference noun is plural, the pronoun must be both plural and objective.
Step 3: Evaluate each option:
- it – singular pronoun, so it does not agree with the plural noun children → incorrect.
- her – singular and feminine, which does not match the plural reference → incorrect.
- them – plural and in the objective case, correctly referring to the children → correct.
- they – plural but in the subject case, not suitable as an object in this phrasal verb → incorrect.