I don't see a problem adding them and as long as the card is in good standing should help their credit ( although I believe a few years ago they changed it so that authorized users has less of an impact than it did for me). I have a Chase account that shows up on my credit report ( credit karma) that my parents added me on when I was around their age. Probably helped me get my first regular credit card as my first card instead of having to get a student/secured one