Good for showing an interest. Good for explaining to your uncle your concerns. Good to explain that their bedroom is just for them just as some things are just his and that it would be wrong for him to bother their things as much as it would be for a stranger to take his. Best to use the "see and flee" approach to teach your son to simply report to you whenever he sees a firearm not being safely used by an adult. He's not supposed to be around a firearm unless a responsible adult is there to control it and he needs to go Mom or Uncle or Aunt about it the moment he sees one. You should also ask Uncle to take the two of you shooting so he sees they are not toys. This should be done frequently enough that your son simply isn't interested any longer in the firearms. If he does persist in having an interest then you have the choice to monitor his movements in the house or move.