Incorrect: Their going to the park tomorrow.
Correct: They're going to the park tomorrow.
Incorrect: There dog is over their .
Correct: Their dog is over there .
Incorrect: I saw there car parked over their.
Correct: I saw their car parked over there .
Incorrect: Their going to have a picnic.
Correct: They're going to have a picnic.
Incorrect: Their planning a trip to Europe.
Correct: They're planning a trip to Europe.
Incorrect: Their happy with their new home.
Correct: They're happy with their new home.
Incorrect: There parents are very proud of them.
Correct: Their parents are very proud of them.
Incorrect: Their going to be late.
Correct: They're going to be late.
Incorrect: They’re teacher gave them a good grade.
Correct: Their teacher gave them a good grade.
Incorrect: There favorite color is blue.
Correct: Their favorite color is blue.
Incorrect: They’re dog likes to play fetch.
Correct: Their dog likes to play fetch.
Incorrect: Their always late for their appointments.
Correct: They're always late for their appointments.
Incorrect: There going to the movies tonight.
Correct: They're going to the movies tonight.
Incorrect: There happy with the results of their test.
Correct: They're happy with the results of their test.
Incorrect: Their going on a trip next week.
Correct: They're going on a trip next week.
Incorrect: Their always polite to their guests.
Correct: They're always polite to their guests.
Incorrect: They’re favorite food is pizza.
Correct: Their favorite food is pizza.
Incorrect: They’re friends are coming over tonight.
Correct: Their friends are coming over tonight.
Incorrect: There sister is a doctor.
Correct: Their sister is a doctor.
Incorrect: They’re dog is very well-behaved.
Correct: Their dog is very well-behaved.