Alphadork
Always starts with teaching them young that they’re a tool, not a toy etc. If it’s not a rifle you’re keeping loaded for home defense, then top shelf and unloaded/lock is best. If it’s for home defense, that’s a little trickier. My thoughts would be bolt locked back, safety on of course, and mounted up under the bed frame. Not an expert on that, and no kids so probably others more knowledgeable there