Childless means having no children. You can say it of a person or of a couple. It is a plain, slightly formal word, and by itself it does not say whether someone wanted children or not. Though actually, some people now like child-free when the choice was theirs, and they keep childless for when they hoped for children but do not have them. Not everyone makes that split, so you will still hear childless used both ways. It never means a smaller child, or not many children. It means none.