My 12 year old was showed a gun and pretended to shoot it at a friend's house last night. I don't know where to go from here.

My son (Mikey) will be 13 in February and is generally a good kid. He was supposed to have some friends sleepover last night for NYE but plans changed and he ended up going to another friend's (Teddy) house instead. There was one other friend, Aiden, who was there as well. Teddy's parents were home but went out to get soda for the boys from a store a couple blocks away. We live in a walkable city so the parents walked.After the parents left Teddy told Aidan and Mikey that one of his presents for his 13th birthday was being allowed to know the combo to the safe. The safe is where the dad stores his gun. He asked the boys if they wanted to see and both boys agreed. Teddy unlocked the safe and the boys took turns handling the gun. It wasn't loaded, according to my son, but I don't really care. They pretended to shoot the gun and played around with it before placing it back in the safe. Teddy's parents came back shortly after and didn't see anything.My son asked me to pick him up at 5am. He was supposed to sleepover but said he was having trouble sleeping. He confessed to me and I don't know what my next steps are. Do I still punish him even though he was honest about it? Will that cause him to hide things from me in the future? I told him I have to tell Teddy's parents and he begged me not to. I told him it isn't safe for Teddy to be playing around with a gun like that and his parents need to know. My son said, "I knew I shouldn't have told you." I'm doing the right thing, right? He is my middle but my older kid never went through anything like this. Don't get me wrong. We had and still have some troubles with the oldest but nothing like this. I am so lost on how to move forward in this situation. via /r/Parenting https://ift.tt/2SN4xsD