First of all, the option should be "his wife," not "his spouse." "Spouse" is a feminist, gender-neutral term that we should avoid using.
In my opinion, the reason you should put your wife first is because if one of your children dies, you can still have more children. On the other hand, if your wife dies, you can't have anymore children (at least not by the same wife). Furthermore, if your wife dies, you become a single father, and this deeply affects all your children.
Maybe it would be different if your wife is post-menopause and your children are all grown up.
In my opinion, the reason you should put your wife first is because if one of your children dies, you can still have more children. On the other hand, if your wife dies, you can't have anymore children (at least not by the same wife). Furthermore, if your wife dies, you become a single father, and this deeply affects all your children.
Maybe it would be different if your wife is post-menopause and your children are all grown up.