J.C.
I would continue to be very friendly toward this family. At the same time, explain to the parents your hesitancy in allowing your children to be in an environment around guns. Don't be critical or judgmental of them for owning guns. Tell them that you are afraid that your children may somehow gain access to the guns. Children are curious and it only takes one time for the adults to be distracted and an accident to happen. This could happen whether it is guns, alcohol, drugs, inappropriate content on television and internet, etc. Don't give up your personal beliefs about this subject. Keep talking to your kids, as well as their friends about safety in general. Allow the children to be friends with this family's children, but try to have your children entertain the friends either in your home or at a public place where you can supervise interaction if needed. If your children feel comfortable in inviting their friends over, then you get to meet the friends and have a better idea of what is going on. Always meet the parents or at least talk to them on the phone before allowing your children to visit their home. Continue to be the wonderful parent that you are.
Best of luck,
J.