Originally Posted by RTWFF

Unfortunately all of the respondents have answered as if you are traveling, but as your OP makes clear it's your parents who are traveling. I've certainly been asked to show a credit card - most recently for TG in Sydney - when I was paying for my partner's ticket and not traveling myself. SQ actually has a question about whether you are travelling at the same time as someone else whose ticket you are buying who is not on a PNR with you. As you'll be there are check-in it might be wise to hang around until they've got their boarding passes safely in hand