If he is already talking to you and his daddy, I don’t think you have anything to worry about. It sounds as though he’s just a bit shy around other people and needs a little reassurance that his contribution will be accepted. If, when others are there, he points to something he wants that you know he can say (“milk,” “go out,” etc.), you might remark calmly, “You can have some milk when you ask for it.” Don’t make a big deal out of it and try to be casual about his reaction. If he gets too frustrated when you try that, try not to give in, and work out a compromise: “Here, you can have some juice.”
Sometimes, very young children are hesitant to talk if the adults around them are highly verbal - if they’re loud or fast talkers who seem to know how to dominate a conversation. Your son may feel that he doesn’t have a chance in that kind of environment.
In the meantime, do everything you can to encourage his language when you are with him. Talk to him a great deal; read him one or more books every day and let him point to pictures he knows; encourage him to imitate sounds or words that you use, etc. He’ll get up his courage to become a public speaker as he becomes more confident of his own abilities to communicate.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.