birds bees kids
Somehow I get the impression you are a single mother so there won't be a father to help with this age-old question. It seems that even with a father around, the mother takes the responsibility to impart her wisdom on the kids.
First you have to ask yourself how did I learn? What was the communications your parents gave you about their relationship together? What cues or messages did you get about what was going on between them? Were they physical with lots of touching, hugging and kisses in front of the children? If so, do you remember the effect it had on you as a child? Chances are, you took it all for granted. They loved one another and no other explanation was necessary. In this environment, Kids, depending on age, may be told truthfully about sex as questions emerge.
If open communications are usual in your family it shouldn't be difficult to talk about in an open way without embarrassment or trauma to the child. There are some good books your librarian can recommend for kids that you may read along with your child.
Of course there are the extreme homes, ones I have heard about as a counselor that would curl your hair. Homes that avoid the subject altogether or describe sex only in gutter terms, leaving children confused and with little in the way of coping skills they need in the course of growing into young adults. It is no picnic for kids to grow with the notion that sex is dirty. No information at all would be preferable.
The rule of thumb is provide information they may understand at their age. Graphic details aren't necessary. You will find that they are soon enough bored and ready to quickly move on. If you keep good communication with your kids, they will bring their questions home from school or the mall where they pick up information(usually wrong) that is more suitably taught at home. Television is the absolute last place for a child to learn anything about male-female interaction or sex. What they learn is that exploitation of females is normal and desirable. Boys are depicted as slow, interested only in sports and sex as it may promote their masculine image. They are seen as loud beer drinking, obnoxious bores.
There is one exception that provides suitable teaching and that is national public television or radio. Some homes restrict network shows altogether for their children and praise the virtues of programming considerate of diverse cultures and splendid story telling and music.
Schools and some churches have some helpful, early childhood education information readily available that deals with improper adult touch. there are peer children's groups that perform in schools, providing examples of "good and bad touch skits" and how to avoid uncomfortable situations. Parents can be comfortable talking with kids about possible adult-child encounters and avoidance. If they can't avoid, they may make noise, which is the enemy of a potential perpetrator. Next, they are taught to get away and report it immediately. Possible harm to a fully informed child may be minimized and the molester brought to the attention of authorities before he may harm another victim.
Informed parents may be prepared and not dread the day the inevitable question comes out of Suzie's room: Mom! "where did I come from?"