I am receiving so many questions about this that I felt it might be useful to create a post about it.
In Rune Factory 2, when your wife becomes pregnant shortly after your marriage, you will have the opportunity to choose the gender of your Child. You can choose to have a boy or a girl or leave the choice to 'destiny' (50% chance either way obviously).
There are only two possible Children in this game: a boy and a girl. Their appearance is set. Marrying a half-elf will not affect that.
The game where the appearance AND personality of your Child will vary according to your choice of spouse is Tree of Tranquility. In THAT game, there is an individual child for each character.
Even in ToT, however, when you choose to start a 2nd Generation game, the Child will revert to the default character of either gender. It is only in the 1st Generation of ToT that your child will have an individual appearance and personality based on your choice of Spouse.
In the following, you can see both the Girl and the Boy characters on the 2nd Generation Start Page. I added some of the Outfit changes for the Girl as well.
(If any one ever wonders why the camera is so jumpy and the movements of my character so clumsy in videos, it is because I am left-handed and everything is designed for right-handed users.)