Try buying some good children’s books that are written for the age group. No sense reinventing the wheel. She will get a good sense of what is the right amount from reading some of those. But we tend to just talk normally, not dumbed down, and our children will pick out what they can get from it. If they need to ask they do, but our 15 mos. old understands like a champ even though she only says a couple of words.