One way to prevent overfeeding of your baby is to let your care provider know that it's OK for them to save and reheat a bottle that your baby has started.

There is a small body of evidence demonstrating that this is OK - really just one unpublished thesis, and the experience of the many moms who have done it. If you're not comfortable with this, then don't reheat bottles. However, in my totally biased opinion, I think it's OK to do - once. When the bottle goes around for the second time, I would say toss it. And never reheat milk that was previously frozen. Thawed breastmilk has lost many of the living immune cells that prevent contamination, and should be treated more like formula in terms of preventing bacterial growth.

Your child care provider may be reluctant to reheat a bottle - they've been trained in formula-feeding, and it's absolutely true that formula can very easily become contaminated, and it has nothing to prevent the growth of bacteria. However, breastmilk is very different - in addition to the living immune cells that actively attack bacteria, it also contains numerous anti-bacterial enzymes. In short, it's good stuff.

Here is the evidence from Ruth Lawrence, MD and Jan Barger, RN, MA, IBCLC - summarized nicely at kellymom.com