My 12 yr old daughter has a stache. It has bothered her for yrs. About 3 yrs ago, I got a little battery powered razor called "Perfect Touch" (I think that is the name) from Walgreen's for about $10. She uses this when she feels the need. The hair has not been coming back thicker or darker. It has worked for us.
I went as far as taking her to a laser hair removal place but she is too young for that right now. I didn't want to risk any permanent damage.
Hope this helps!
Susan
PS......YEAH school is almost in!! We are taking our last hurrah for the summer later this week to FL. I can't believe it but we are taking an extra 12 yr old along with us, YIKES, but it will be fun!!! Moms will get the routine back soon!