Beginning a conversation about sexuality early and continuing that conversation as the child grows is the best sex education strategy. It lets parents avoid giving one big talk when the child reaches adolescence, when they may think they already have the information and won’t be receptive. When talking to your kids about sex, it’s important to explain things in a way that your child can understand, given their age and level of development. 

Here are some facts about talking to young kids about sex ed :

• You don’t need to know all the answers. It’s perfectly fine if you don’t always have the answers. In fact, one really powerful way to build your relationship with your kid is to say, “That’s a great question! I don’t know the answer but how about we look it up together?”
• There are no gender rules when it comes to conversations. Moms can talk to sons and dads can talk to daughters about health and bodies. In fact, being able to have conversations irrespective of gender will help your kid develop an inclusive frame of mind in other domains too.
• You need to talk to young kids about consent, and it’s a lot simper than you think. Early on, consent conversations have nothing to do about sex; it’s all about bodily autonomy and teaching kids to know their own boundaries and respect other people’s boundaries (e.g. hugs are not mandatory).

Reference : https://4hatsandfrugal.com/wp-content/uploads/2019/04/Talking-sex-with-a-4-year-old-AMAZE.png