Triple threat time.
- The word their is a possessive adjective that shows that something belongs to them.
- They're is a contraction for they are. The apostrophe stands in for the missing A.
- There can be a lot of things: noun, adverb, interjection, adjective, or pronoun; it usually means "[in] that place."
Example 1
Don't sit there! The kids' imaginary friend is on that seat and they're going to flip if their BFF Bubbleface gets squished.
What a beautiful sentence. Translated, it reads like this:
Don't sit in that place! The kids' imaginary friend is on that seat and they are going to flip if the kids' BFF Bubbleface gets squished.