Explanation
In the sentence "Children were making love castle",
the word "making" is a verb, but specifically, it functions as a main verb in the sentence
Verb: "Making" is a form of the verb "make," indicating an action.
Main verb: "Making" is the main verb, part of the verb phrase "were making."
The structure of the sentence is the past continuous tense (with the auxiliary verb "were" and the main verb "making").
NOTE
Why "making" is not a gerund:
A gerund is the -ing form of a verb that functions as a noun.
For example, in the sentence "Making love castles is fun," "making" would be a gerund, as it is the subject of the sentence.
However, in your example, "making" is describing an action, not functioning as a noun.
