How do I tell my boyfriend that I have a two year old son?

Is your boyfriend sixteen as well? If he is, then you should talk to him somewhere private, and not at your place. Don't bring your son, make it just you and him. Tell him you have something important to talk about, and then tell him. Assure him that you do not expect him to take care of the kid, especially since you two are just dating and in high school. Tell him that it doesn't change your relationship, but that you thought it best that he knew. And then just go from there. He will either approve or he won't, an he will probably be grateful that you told him and didn't let someone else do it.