My pediatrician told always to ask when going to a relative or friends house whether they have a gun and how they handle it (locked, loaded, etc). She says this is as much a public health issue as carseat safety, dog bite safety, and keeping the kids away from sharp knives.
My one year old son (this was 3.5 years ago) found a gun my grandfather left under a throw pillow on the couch (grrrr....) and Ben PUT THE HANDLE IN HIS MOUTH.
The gun wasn't loaded, but the safety was off, and...thank God we weren't the lead story on the local news station that Thanksgiving. ("Toddler shoots self in mouth in freak tragedy on Thanksgiving...")
Say something, and be firm. No vacation if gun safety isn't priority #1. Period.
Best of luck to you,