No These do not have an adjustable waist... My son has a tiny waste and was ok with a belt. I have sweat pants with adjustable waist on here somewhere great condition :)
I'm sorry, I really have no idea lol I do not have the knowledge of a seamstress the tag just says size 10 My son is super skinny and tall . I took a measuring tape and measured it from hip to hip in the front and it reads 14 in. Hope that helps :)