Telling them the truth nurtures self-esteem and gives them the message that they are worthy of respect. When you teach your children to use correct names for parts of the body, they learn to respect their bodies and to see you as a trusted source of information. Self-touching is common and normal. Children will touch parts of the body because they are curious, just as they explore aspects of their environment. Explain that touching and rubbing one's own genitals is called masturbation.
Masturbation is one way people express their sexuality, and it is a normal part of growing up.
It is natural to be curious about your own body and to explore its sensations. Teach your child that this behavior is private, just as using the bathroom is private. It's good to be curious about these things. You can learn correct words from me. You are fine just the way you are.