Boyfriends.
My four year old daughter said to her 20 year old brother...
Ohhhh baby, we should get married.
This is something she heard me say to my wife a few times.
Kids pick stuff up, and if we can give them sound Godly advice it will stick with them, and they will associate that advice when the subject comes up again.
Certainly I need to watch what I say around my daughter, my fault on that one.
Just tell the kid that a boyfriend is someone that is your close friend and a boy. Same with a girl. Just means you hang together more often.
By developing and addressing these concepts early, we can ingrain in them a right thinking about things as opposed to what the World thinks, making them strong in the Lord, keeping the truth in what is right.
Jesus Is Lord.