Isn't it the other way around? Someone who mends their own clothes looks capable, creative, and economical. Also, elbow patches are trendy.
Of course there is a difference between mending otherwise fine clothing and having to go on wearing worn or threadbare clothes, as you rightly point out.
People who are confident and strong can definitely pull off mended clothes. On the other hand, it's not wise to hand your children obviously mended stuff if you know that they already struggle socially. Bullies sense the weak ones and attacks based on clothing are common, also in later life (although this phenomenon peaks at school).
Of course there is a difference between mending otherwise fine clothing and having to go on wearing worn or threadbare clothes, as you rightly point out.