I know the fashunz police like to go on and on about some supposed "air travel etiquette" and how appalling it is to wear sweats (or something other than jeans/chinos and a sports coat but fuck you if I have to sit on a 6 hour flight followed by a 14 hour flight with my almost 3-year old son you better believe I'm wearing sweats and it's not because I've "given up", it's because I'm going to do everything I can to remain comfortable.
I've done this, and I always wear jeans. I also have a daughter under 7, and one under 5. There are also a lot of good looking technical pants, if that's your thing. I mean, if you want to wear sweats, it's not like I am going to pants you in the middle of the terminal, or point and scream at you, or even give you a second look, and it's not "unacceptable" in any way. But I do think that it looks dumb.