I remember my older child telling me he wanted to marry a classmate when they were around 6 or 7. My response was to explain that he couldn't legally until he was 16 with parental permission, or 18 without, and that this was some way off. But that if they still wanted to be married when they were 16 I would certainly support them and talk to the other parents. And this led on to discussion of other things where the law has age limits, like voting and driving.