Kids who"夜晚要食住奶先肯訓" is very easy to hv teeth decay. My son's front teeth was turning grey due to the same reason when he was 1.5 yrs old. My dentist said he can't help return them in white since he are too young to have "repair", only I can do is having his night bottle earlier and having his teeth brushing everynight after the bottle.
My son refused teeth brushing during that period, then I kept cleaning his teeth after every meal (lunch, dinner, milk...)by my finger with a wet cloth wrapped around. Now he is 27m too, and he accepted teeth brushing 3 months ago. His front teeth cannot recover with white color, but don't get worser then before.
You may also consult to your dentist on how to take care of baby's teeth.
Some mothers wonder why do their kids who have teeth brushing every morning and evening still have decay, because 1. too much junk food between normal meals, 2. always let the kids sip the drink (i.e. the kids sip one month of the drink and then go away to play, come back to sip another month after a while and then go to play again, and so on...)
After I understood that, I intend to serve my son snack in right time and keep him with bottle for sugary liquids (juice, herbal tea etc), because it can make him finish the drink quickly from laying down to enjoy the bottle. To avoid decay, I don't prefer weaning bottle too early.
One more thing my dentist reminded: If moms used to serve kids with fruit dish after dinner or lunch, just serve after the meal immediately. A break between the meal and the fruit dish is not necessary and is one of the easy way to have decay.