How do you talk to them about design?
But at this age, it is the origin of their existence more than the sexual relationship that intrigues them. Parents must start talking to them about anatomy, but also about love. They can answer that when two adults love each other and want to have a baby, they make a big hug during which "the dad puts the little seed in the belly of the mother". This explanation has the effect of reassuring the child who knows, by this means, that he was desired. Later, around the age of 6, parents can simply say that during sexual intercourse, the father's penis enters the mother's vagina and the sperm that flows from the penis contains the sperm that must meet the ovum to fertilize it. But needless to be too technical: the child retains only what his ability to understand allows him to assimilate.
Should we talk about pleasure?
When they understand where the babies come from, the children then wonder about the relational dimension of the sexual relationship: they ask how we make love, if it hurts ... Their talk of pleasure must be natural, telling them that adults make love just because it's good. This allows them to (re) hear that they are the result of an act of love, but also to gradually distinguish between sexuality and reproduction.
How to react to masturbation and sexual games?
The practice of masturbation is very common in early childhood: it serves as much to give pleasure as to reassure oneself. Parents must not forbid it, because to condemn it by making the child feel guilty would risk associating in their spirit enjoyment and forbidden. The best reaction is to explain that this pleasure is normal but reserved for intimacy. As for sex games, you do not need to be alarmed: by playing the "doctor", "touch-pee" or "dad-mom", children just want to check what they have understood. These mutual observations are not reprehensible until all the children feel "forced" to play.