We have LL bean sweats for my average height 7 yr old DD and they still kind of bag around her ankles, so I think they'd work well for a taller kid. They have a real drawstring which helps for a really skinny kid (so many sweat pants for kids don't have true drawstrings, it's just for show, or they'll have elastic but it's not snug enough).
I'd also check primary, which I've found to run slim and long.