身外物。自尊心和穿着的关系不大吧。

I wore my father's sweaters during my high school years and did not have my first pair of jeans till senior year in college. My boyfriend then told me to wear something more like girl. I think I am a pretty confident person.
teach kids to be meat and clean, choose good quality with good price (no need to be brand name and expensive), teach kids to respect themselves and do not judge people by what they are wearing. And it is not a shame to wear non-brandname clothes.

This is more useful to build confident than buying expensive clothes.