We got fat during our vacation. In this sentence we use got because got is the second form of get. We can't use have grown due to its first form of verb. In the above question, they asked us to use past participle which means second form of verb in the sentence and we know that got is the second form of verb so that's why we can use got fat word instead of have grown in the sentence.
As soon as their able to make full on sentences, parents will usually start transitioning them into using honorifics so they can properly talk to older folks.
