During or before toddler days, your child undoubtedly discovered that touching the genital area felt good, and you may have been dismayed to see little hands exploring inside the diaper zone (whether clean or otherwise) on a number of occasions.
This type of exploration and ongoing curiosity about body parts is common and quite normal in young children. Questions about where they (or their siblings) came from are part of the same package. When it comes to dealing with such sensitive areas and topics, you have a number of important assignments:
Make it clear that you are the prime source of information about these matters — and not the kid next door or some other unreliable source. Be levelheaded, honest, calm, and straightforward when you name body parts and explain what they do. Using actual terms (penis and vagina) and not more colorful vocabulary may save some embarrassment later on if your child happens to make a public pronouncement. This information by itself doesn't jeopardize your child's innocence.
Instill respect for the body your child has been given, the Creator who made it, and the functions it performs. This means that you should not communicate a sense of shame or repulsion about any part of your child's (or your own) anatomy. It also means that you need to teach what, where, when, and how it is appropriate to touch or talk about these areas.
Your child needs to know that these are things to discuss at home with Mom and/or Dad and not with other kids in the neighborhood. If you discover him and a playmate checking out each other's pelvic area, don't panic. This is also normal curiosity at work, and he just needs a brushup on the ground rules.
Remind him that these areas of his body are just for himself, his parents, and his doctor to see, and not other people. Tell your child that if someone else tries to touch those areas, he should protest noisily, get away, and tell you as soon as possible. He must know that you will not be angry or upset with him if this should happen.
Release information on a need-to-know basis. Your child does not need to hear everything about reproduction in one sitting and will be overwhelmed (or bored) if you try to explain too much at once.
Respond forthrightly with a minimum of fluster when your child cuts loose with offensive language that he didn't hear from you. Our culture is flooded with off-color messages and images that degrade the beauty and wonder of sexuality, and you will not be able to keep your child completely insulated from such negative input.
As a result, he may pick up some R-rated expressions in the neighborhood, even at this young age. (Be sure, by the way, that what you say or the language you allow in your home isn't in any way inspiring this unpleasant verbiage.)
If this occurs, stay calm. It is unlikely that he even understands what he just said, as a simple quiz ("Do you know what that means?") will often confirm. He is far more likely to be interested in the power of words to create a stir than in actually expressing some specific sexual or crude sentiment.
Without sounding alarmed or flustered, explain that the words he just used are not ones that you use in your family and that he needs to stop saying them in your home or anywhere else. You should emphasize that such words and expressions put down other people and can make them feel upset or even afraid.
If your child's new expressions include casual or inappropriate use of the words God or Jesus, a simple explanation about the importance of respecting those names will be needed as well.
Once you have stated your case, be sure to take appropriate action if you hear a repeat performance. If he persists after one or two reminders, let him know that a consequence will follow next time, and then carry it out if needed. If your child begins using harsh or obscene language, you need to not only retrain his vocabulary quickly and decisively but also have a frank conversation with whomever you determine to be the source.