Officers say the injury came from the recoil of the gun, and no one else was injured.
The bullet landed in the church wall.
Police and gun experts say it's an accident that is easily prevented.
Police say the handgun was placed under the driver's seat. When the child's father went inside to drop off another child, the 4-year-old found the gun and fired it.
One certified gun instructor says it sounds like the classic case of a careless or irresponsible gun owner.
Authorities say the scene on Kmart Drive Monday morning could have been the scene of something much more tragic.
“Number one don't leave small children alone anywhere. Small children are curious. They're notorious for getting into things they shouldn't get into,” says Jeff Hughes with the WFPD.
But leaving a child in the car was not the only mistake made Monday morning- a loaded and unsecured handgun was in arms reach of a child.
“If it's a handgun, it has to be concealed. And with or without a permit you can have a gun in your vehicle but you are also required to keep it secure,” says Point Blank CHL Owner Chris Reitsma.
And that means certain steps need to followed.
“Concealed means no one can look in the window and see a gun. Rifles do not have to be concealed, only handguns. Secure means either on your person in your possession or if you're away from the vehicle it has to be locked up so a child can not gain access to it,” says Reitsma.
It is unclear if charges will be filed in this case and it is still under investigation. But there are some options if charges are filed.
“If a child gains access to a fire arm, it's a class C misdemeanor if the child discharges the firearm and causes death or serious bodily injury, it turns into a class A misdemeanor,” says Reitsma.
He says locking your gun away from children is the first step to keeping them safe. But it's also important to teach them gun safety.
“Hiding it is the absolute worst. You never want to hide it and you never want to keep it a secret. You teach them as young as you feel comfortable teaching them,” says Reitsma.
Again, no one has been arrested and no charges have been filed. Officer Hughes says endangering a child could be an option, but more investigating is needed.
We do not know if the father had a concealed handgun license but police say you are not required to have a CHL to carry a handgun in a car. If you are stopped by police, the law requires you to present a license to the officer if you have one, and if not, you are required to tell the office you have a handgun in the car.
Copyright 2016 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.