This white tee from Old Navy comes in a ton of colors and is SO GOOD. My three oldest girls have been wearing them nonstop this summer (I just popped out of my office and 2 of the 3 of them are wearing them right now). Size up - I’m ALWAYS an XS and sometimes an XXS and I’m a S in this. My 10 year old wears the XXS and my 12 and 14 year old girls wear the XS.