Which of the following sentences uses apostrophes correctly to show possession?

The student's essay was well-researched.

Correct the sentence to include the apostrophe where it is needed: 'The childrens toys were scattered all over the floor.'

The children's toys were scattered all over the floor.

They're going to the store later.

I can correctly use apostrophes to indicate possession and contractions.

1
Apostrophes are used to show the omission of letters in contractions and to show possession or ownership.
2
To show possession for singular nouns, add an apostrophe before the S, and for regular plural nouns, add an apostrophe after the S.
3
For irregular plural nouns, the apostrophe goes before the S, because adding an 's' to the plural form is incorrect (e.g., the children's toys).