Christy A. Smullen, of Seaford, Delaware, was arrested and faces a number of charges including Endangering the Welfare of a Child.
Police say they were called to the Seaford Volunteer Fire Department around 2:10 p.m. Wednesday.
Once there, officers say they saw two bullet holes in a roll-up style door on the west side of the building.
The investigators say they learned the three year old somehow had gotten a shotgun from the home and brought it to an outside porch.
Police say the shotgun went off, hitting the firehouse door.
The Delaware Division of Family Services responded and placed the child with his father.
Smullen was released on $8,000 secured bond.
Meanwhile, two other women inside the house, Keisha A. Griffith, 39 and Stephanie Brittingham, 36, were found at the home and arrested on outstanding court orders.
The Seaford Police Department reminds everyone to properly lock and secure both their firearms and ammunition in a safe location away from children.