Is children a pural noun or singular?

The Word 'children' is not a pronoun. The Word 'children' is a noun, the plural form for the noun child.

The plural noun children can function as the subject of a sentence or clause, and the object of a verb or a preposition. Examples:

subject: The children are ready for lunch.

object: We brought lunch for the children.

A pronoun is a Word that takes the place of a noun in a sentence. The subject pronoun for children is 'they'; the object pronoun for children is 'them'. Examples:

subject: The children are ready for lunch. Theyare waiting in the cafeteria.

object: We brought lunch for the children. We will serve them right now.