L.G.
Hi M.! I have a 2 1/2 year old daughter and we took her to a pedi dentist at 1 1/2 and again a couple of weeks ago. She also had stains exactly where you are saying and when she went to her first visit they told us that those were from milk. That it sits on their teeth and eats the top layer of their teeth and he used a "dentist" term for it, but I can't remember! He said not to worry (don't ignore a serious problem) but that she will lose these teeth anyways. He also said a lot of children get them, but not to let her drink milk at bedtime to go to sleep and brush her teeth before bedtime and no more food/drinks after brushing. We've followed his rule for the last year and when we took her to her second visit a couple of weeks ago, he said that her teeth look much better and to keep up the good work. I hope this helps!