pants for boys?

I've been lurking for a while and have found so much valuable information on these boards, but now I have a question that doesn't seem to have been asked yet. I bought this pattern specifically because the webpage calls it a "Girl's and boy's pants and top pattern," though the printed pattern only says girls'. My (3 yr old) son is tall and skinny while also being incredibly small for his age, so I know that things usually need to be altered for length, though I have never done much other altering. But there's no way these pants are drafted to accommodate a boy's need of room in the rise... right? I tried holding the front piece up, and it just seemed way too short. Though as I am writing this, I realize that I did not account for the yoke. So has anyone made these pants for a boy? Even if you've made them for a girl, do you think there's enough room? I'd prefer not to make a muslin when the whole pattern won't work.