I worked with a pediatric dentist for several years. If the children fell asleep with a bottle, even milk, they could be more likely to get baby bottle caries. It usually depends on how big and the age of the child if they'll fill them or not. If the tooth with the decay is close to falling out they'll usually watch them, unless they're very deep and may involve the nerve.
I've always heard them tell parents that a deep cavity can spread to the developing tooth bud and even involve that tooth.
Also read that tooth decay bacteria can be spread by kissing. Not suggesting that's how they got them. Just saying there are a number of reasons they could have gotten decay. Neglect isn't always the reason.
Here's an interesting article you can read.
http://www.msnbc.msn.com/id/35989527...cavities-baby/
But, if you're not comfortable with what you were told you should certainly see another dentist. The main difference in a General Dentist and Pediatric Dentist is the size of the instruments. Granted Pediatric Dentists specialize, but they also have smaller instruments. I know a pediatric dentist that used to strap children to a papoose, needed or not. I was sent there to do my clinicals. When I told the instructor about that she never sent a student back there.
Good luck.