We talk to a child about fractions or sexuality in the same way. Of course, the moral misuse of fractions is less of a concern. But just like fractions, we introduce first the idea of half. Then quarters and smaller parts. Then the higher level information is given once the foundation to understand such things are secure.
Eventually, they understand not only the language of fractions, the purpose of fractions, they can explain the nature of fractions to others. They understand the underlying rules and limitations to fractions. If the rules for fractions aren’t followed, everything will be wrong.
So it goes. We start, very casually in circumstances that present themselves to talk to our children about sexuality. About how their body works, how a baby grows in the womb. About how different types of plants and animals reproduce. When they are young, the information is so easy to give, and it becomes the foundation for our later conversations.
So, if child is learning the “facts of life” and learning the laws of God at the same time, over the years they are given to us, and how our love for Him is manifested in our obedience and desire to do His will, the two paths of formations and information will meet.
Understanding will deepen, and the layers of knowledge about sexuality, and about God will mature.
We don’t wait until the child hit puberty to suddenly tell them about God. We provide small talks whenever the opportunity arises. Layers of knowledge and understanding build in the natural cycle of learning.