My teen daughter 16 and son 19 are acting weird?

I think they are getting to Intimate with each other she usually sits on the couch with her head resting on his shoulder and sleeping together. They talk in a flirty manner and bring me into like ; mum Raye has taken the remote off me giggling manner. and I wouldnt breathe a word to this to anyone but on the same couch they where fully clothed and I saw them rubbing their genitals of eachother