Well, first off, I wouldn't have her providing day care for my children if this is what's going on. She can't be trusted to care for them properly. She may be drinking during the day and hiding it. Suppose one of the kids had an accident and she had to drive them to the ER? And many alcoholics overestimate their ability to drive when they have alcohol in their systems.
You could be right that she started to drink because her life is unhappy, but once you get to the point where she apparently is (hiding bottles etc.) then simply changing the life circumstances won't remedy the alcoholism--that's there for good.
You can certainly express your concerns to her, but I wouldn't expect a particularly receptive response. Especially if you don't want her caring for the kids any more. She is likely to heap a huge amount of guilt and anger on you and your wife. But the safety of your kids has to take priority over her wounded feelings. Even if it feels like you're causing family drama, it's your job to endure that if it's necessary to protect your children. You can tell her she's welcome to spend time with them at your house, but as long as her drinking remains unaddressed you are not comfortable leaving the kids in her care.
Obviously this is something you need to discuss with your wife, but it's something that must be done.