If I don't have any kids, do I need to keep guns locked in a safe or can I just keep them laying around in a place I choose, loaded or unloaded?

Your house, your rules.

1 minute ago, Ray Ray said:

Your house, your rules.

Do those rules change if there is an under-18 visiting? How do they change?

Just now, jasonx said:

Do those rules change if there is an under-18 visiting? How do they change?

Your house, your rules.

3 minutes ago, jasonx said:

Do those rules change if there is an under-18 visiting? How do they change?

NJ law is that you cannot allow a minor easy access to a loaded firearm.

Therefore if a minor is in your house by your permission, you can leave the guns laying around if there is no ammo available.

You can leave ammo around if the are no guns available.

You cannot leave guns and ammo around at the same time.

Minor meaning <14 YOA.

If you want to keep your firearm locked up and still be able to access it quickly VAULTEK makes some really nice biometric safes. 

As stated above, no legal requirement to keep them locked if no minors will have access, HOWEVER:

Home burglaries are a huge source of guns that get used in crimes.  A bolted down floor safe greatly reduces the chance that your firearm(s) will be stolen if your home is broken into.