How to disable the previous child object of a parent,How to disable previous child of a gameobject

Essentially im using a gameobject to store guns that the player has access to and there is a script that allows the player to pickup a weapon. however when the player picks up the weapon it doesnt disable the previous gameobject of the parent so the guns just pile on top of each other. Sorry for the bad explination How can this be done Any help would be apreciated :)