Fill in the blank with a suitable preposition.
I looked _______ the children while my friends were out.
The prepositions ‘at’, ‘after’ and ‘for’ are commonly used after the verb ‘look’ to denote various things. ‘Looked at’ means to point one’s eyes towards something. ‘Looked after’ means to take care of someone/something. Whereas ‘looked for’ means trying to find something. In the given sentence the speaker is taking care of the kids after her kids left, therefore option C is correct. Although ‘looked at’ and ‘looked for’ are grammatically correct the meaning of the sentence would change and the sentence would become illogical when we use ‘at’ and ‘for’. Therefore options A and B are incorrect. The preposition ‘by’ is used to denote a place that is near another place or the agent of an action. Since the children are neither a place to look nearby or the agents of the action option D is incorrect.