OK Let's review: 'Their' means something which belongs to some one. "I like their chickens." 'They're' means they are as in "They are crazy about chickens." 'There' means a place. "My chickens are over there!" Seen instead of have seen. I have seen those chickens before . I saw those chickens yesterday. If the word "seen" is in the sentence as a verb there must be a "have" in there too. OK class all done now! Get back to your chickens!