Lori Conley, who is in her 40s, pleaded guilty to involuntary manslaughter, child endangerment and tampering with evidence at a court in Franklin County, Ohio, on Monday.
She was looking after Haddix Mulkey, who was eight months old, at her suburban home in Columbus on May 13, 2016 along with seven other infants left in her care.
In an attempt to try and get him to sleep, Conley gave the baby an adult dose of Benadryl, an over-the-counter allergy medication.
After finding him unresponsive, Conley called 911 and Haddix was rushed to hospital.
However, authorities say he tragically died that same day from the overdose.
After pleading guilty to the charges, Conley, who was operating a daycare at the residence without a licence, now faces up to 17 years in prison for the death of the baby.