Guns kept in a car usually aren’t required to be locked up if the car itself is locked.
This varies widely from state to state, with different requirements for loaded vs unloaded, concealed carry permits, and accessibility requirements.
There’s not much point having a gun in the car if you have to ask the carjacker to wait nicely while you fetch your gun from its locked container.
So use a quick-access safe mounted in the vehicle or get a concealed carry license and keep it secured in a holster with you. No excuse for leaving it accessible to a child.