Supervision. Toddlers require your full attention. If you are impaired or unconscious from drinking, you cannot adequately supervise your child. This is criminal negligence. Your child could wander into traffic, be injured in a home accident, or be abducted. Even basic care duties like preparing meals and changing diapers can be affected. You cannot function as a parent when abusing alcohol.
In many ways. A mom who has a drinking problem can raise a toddler who can suffer from mom's drinking in profound and serious ways. The intoxication by mom can interfere with the normal attachment and bonding process. Once this occurs, it isn't really possible to go back and have a "do over." also, an intoxicated mom will not always be as "available" to the child in times of need or distress causing neglect.