Your child will learn a great deal about sex and sexuality from you as a parent whether you want that to be the case or not. If you behave as though the conception of your child was from a miraculous one time sexual event, show not open affection for your partner, and never talk about sex or intimacy they will learn that you don’t want to talk about sex or hear their feelings or concerns about sexuality. It’s unlikely in this situation that you are the person they will seek out to ask questions or express concerns. If you are openly affectionate to your partner, talk about sexual topics when they present themselves as teachable moments, and ask your child about their feelings in these situations it’s likely that they will feel more comfortable approaching your with concerns or at least responding to questions you ask them about their feelings.
The first thing to clarify is what are your expectations and aspirations for your child. This may range from expecting abstinence until marriage to expecting sexual activity at a young age and hoping for responsible contraception and STD precautions. There are many places between these two examples that may better describe your expectations. Having an open discussion between you and your partner if appropriate can be very helpful as a starting point for understanding your own values.
Once you have realistically and objectively described your own values and hopes for your child regarding sex, then you are in a position to take steps to help your child understand your expectations and internalize your values. Sex education is very important in the development of ever single person.