My kids may have their own money, but they're not allowed to buy what they want unless I approve of it. Since it's their money, should I allow them to get a shirt with questionable language on it? Same should go for questionable size, length, etc.
I know it's a "pick your battles" kind of thing, but I'm sorry - at age 13, sending my child out in clothes that aren't the correct size for them is a battle I'd fight, ESPECIALLY since kids at school are cruel and will point out the rolls, bulges, etc.