Hmmm...I'm not sure what the white spots could be, maybe calcification?
I had to get crowns put on my oldest sons two front teeth when he was 16 months

It was awful, and if I knew better then , I would have just waited. He ended up going back to a different dentist at 2yo for a brown spot on his other teeth, and that dentist said his fron teeth porbably didn't even have cavities, just staining


He also said it was probably caused from a tooth infection I had when I was pregnant, that I took antibiotics for. What a relief, when I had three other dentists telling me it was from nursing.
Anyway, know that its not from nursing, or not brushing teeth (although its probably a good idea to start that) Most likely its a bacteria that is passed from mother to child during pregnancy.
And if you go to the dentist, make sure to get a second opinion.