Since most young children can only take in small bits of information at any one time, they won't learn all they need to know about a particular topic from a single discussion. That's why it's important to let a little time pass, then ask the child to tell you what she remembers about your conversation. This will help you correct any misconceptions and fill in missing facts.
Finally, in an effort to absorb all they want to know, children often ask questions again and again over time -- which can test any parent's nerves. But such repetition is perfectly normal, so be prepared and tolerant. Don't be afraid to initiate discussions repeatedly, either. Patience and persistence will serve you and your child well.