Please Help!Tooth decay in a toddler

Hello,
My son is now almost 14 months and my husband and I noticed that two of this upper teeth (not the biggest ones) have an enamel that has worm away exposeing the more delicate lighter area of the teeth. He does nurse and I read that nursing actually helps protect the teeth and is un likley to cause decay because the baby swallows the milk un like a bottle where the milk can pool upwards. I think this probem is attributed to us not brushing his teeth like we should. We actually just started to brush his teeth and he persists. I wonder if we would of started brushing his teeth at the first on set of a tooth if that would of prevented this in the first place. I also read that some people are more prone to tooth decay. Well I don't know what to do now- we are brushing his teeth twice a day whether he likes it or not because we don't want to see any more damage. We don't have insurance so what can we do??? We are first time parents so everyting is still new to us. After being married for 8 years we got pregnant and we are still so new at parenthood. Can the worn away enamel grow back or is the tooth doomed???????????????????????????This has been weighing on my mind. Should we give him calcium supplments to help make his teeth stronger??? We can't give him cows milk because he is allergic to it- it causes him to break out in severe eczema. I removed it from my diet and his eczema cleared up. Also I have read that cows milk is not all is hiped up to be besides the calcium factor. Please help

Thank you
Sarah Tweet