The beauty of consent & bodily autonomy is that the conversations are always evolving and adapting when children grow their experiences do too. Talking about consent, personal boundaries, and respect never end!
Learning how to install those ideals in your child is hard, these are a few ways you can.
It can start with narrating diaper changes for infants, you can tell them what you're doing and why and then seek permission to change them as they become vocal toddlers. You can be explaining why the doctor wants to do an exam, empower your child to decline to have parts of it performed, such as genital exams, if they don't want them done and are otherwise healthy. If they are needed explain that to them and explain what's going on as it happens.
You can ask your children before you show physical affection, explaining that we ask people if we can hug them, hold their hands, or give them a kiss, and before expressing other kinds of affection like high fives, handshakes, and air kisses/blowing kisses because some of our friends don't want close body contact like hugs.
You can have conversations about how touching and being touched anywhere on our body is never a "secret" and we never have to be touched or touch others in ways that don't feel okay or that hurt.
These conversations evolve at different rates for different kids. Some kids might want to know more about sexual contact after hearing or reading more advanced explanations of heterosexual conception; while other kids don't want to really know anything until their body and hormones start making them feel differently about their peers during puberty. We think it's more important to equip parents and other adults with the tools to talk about the basic principles of consent, boundaries, autonomy, respect, and pleasure then overwhelming children with “the sex talk”. Other details can always be looked up or filled in as topics arise.