Sgt. Kim Judy resigned from the Emmett Police Department in a letter to the police chief on Friday.
"I am leaving to find other employment and to defend the criminal allegations that have been made against me, as to not involve my relationship with the Police Department," the letter states.
Officials say a 3-year-old was handling Sgt. Judy's gun when it went off. The bullet hit the toddler, another child and their mother. All suffered minor injuries.
On Tuesday, the Ada County Prosecutor's office says Judy was charged with two counts of felony injury to a child. She was arrested by Idaho State Police Tuesday morning.
Prosecutors also say Whysper Rowden, 20, was also charged and arrested on the two felonies. Both were booked into the Canyon County Jail.