Ay, nakikita ko yan sa iba rin ng bata, lalo na kung may iron-rich vitamins o multivitamins na malalim ang kulay! Minsan din kasi ang vitamin stains ay parang permanent-looking pero pwedeng i-clean lang ng dentist, or sometimes it's mineral buildup from the water rin. I'd suggest asking your pediatrician or dentist kung talaga ba yun from the vitamins, kasi may ibang reasons din kung bakit dumarken ang baby teeth, at they can check kung may other causes na dapat bantayan. Pero sa amin, one of my mum friends na may ganitong situation ay nag-switch sa different brand of vitamins at nawala na yung discoloration eventually.