How do you know if your son or daughter is gay?.. Just based on what they're sharing, if you are wondering if they are questioning, sometimes you just have to ask, "What's going on?"  And, if they say they like someone, don't assume the person they like is a boy or the person they like is a girl.  Maybe you ask "who is it?"  "What are they like?"  And, if you can't figure it out then, then maybe you need to just ask.  But if you're wondering, you are probably wondering for a reason, and there probably is something going on.
The other thing is, there's so much in the media about questioning or bisexuality, especially for girls.  It's kind of cool at parties.  Sorry parents if you want to cringe right now, but it's cool at parties sometimes for girls to make out with each other because it's something to do. So you kiss your best friend and the boys think it's cool.  Suddenly you got a lot cooler in your friend group. This isn't everyone, and this isn't necessarily a reflection at all about their sexuality.  This is about attention. This is about getting other people to notice me. But, it's also a really good conversation to have because it's still potentially acting out in a sexual manner, that might be unhealthy.  It might not be good for you to do that because you're not doing it for the right  reasons.  You wouldn't want your son or daughter kissing a boy or girl-- depending on if we're talking about heterosexuality-- you wouldn't want to put them in that situation so people can watch.  That would seem strange.  But  right now, sexual acts in general with teens-- it's a lot more casual. Again, parents don't flip-- it's not all teens, it's not.  But, your teen does know teens who are [same-sex kissing for attention].  So, there's two different sides-- if you're wondering if your child is questioning their own sexuality-- if he or she could be gay-- then the other side might be going out and getting some education, going out into a  community center and getting some knowledge and learning tools if you don't have the knowledge.  One thing I really encourage parents-- know what your internal clock says, how you feel.  If you're saying to yourself-- If my son or daughter is gay, I'm okay with that, and does your child know that?  If they do, they'll talk to you about it. If they don't think it's going to be okay, they're not going to talk to you.