Three to Four Years Old
By this age children are aware of gender differences. They peek under each other's clothing. Don't panic! It's normal behaviour for an enquiring little mind. They like to undress their dolls and check the bottoms of pets. They begin to repeat swear words and have fun with toilet humour. They are not embarrassed to use words like "penis" and "vagina" unless their parents are.
At this age children may enjoy masturbating. This is a good time to start teaching them about public and private behaviour.
This is also a good time to start talking about public and private body parts and wanted and unwanted touching.
Reinforce the facts of reproduction, in simple terms, when the chance arises. For example, if you see a pregnant woman bring up the issue of pregnancy and how a baby grows inside a woman's tummy.
Reinforce teaching with books and illustrations.
Remember the way you say something tells them more than what you say - try to sound gentle.