Question

Rewrite each phrase into a sentence using a possessive noun and correct punctuation.

toys belonging to the children

Answer 1

You could start with "The children's toys ..."
"children's" would be the possessive noun.

Answer 2

"The children's toys"

Answer 3

There needs to be a verb added to have a sentence, such as
"The children's toys fell."

Answer 4

"Who's toys?"
"The children's toys."
Complete sentence.

Answer 5

That answers the question, but it is not a complete sentence by itself.