Are boy and girl a pronoun?

No, the Words 'boy' and 'girl' are nouns, they are Words for people.

A pronoun is a Word that takes the place of a noun in a sentence.

The pronouns that take the place of the noun 'boy' are heas a subject and him as an object in a sentence.

Example: The boy sat down to lunch. He ate a tuna sandwich that he had brought with him.

The pronouns that take the place of the noun 'girl' are she as a subject and her as an object in a sentence.

Example: The girl likes to play the piano. Shetakes lessons twice a week. I often hear her playing.