I agree with the "don't sell" comments. Of course, you need to talk this over with your gilfriend, but having a gun in the home with does not have to be a huge issue.
Get a gun safe. If you're still unsure, get a cable lock (at least in CA, all XDs come with one standard). If you're still unsure, store the ammo and mags in a separate, locked container. Sure, as you get "safer", the accessibility in need diminishes, but since you're willing to sell, I would think that you'd be OK with a little less access.
At eight, the boy should be old enough to "handle" knowing about a gun in the home. This is actually a great opportunity to teach the kid about gun safety. This will not only keep in safe in your home, but in the rest of the world, where a firearm might be unsecured (e.g. friend's house, etc.). Also, allowing him to see/handle the weapon will help dispel a lot of his curiosity about guns, which will also make him safer overall.
Learn about the Eddie the Eagle program through the NRA. Basically, it boils down to four very gun-neutral instructions for kids upon finding a firearm:
1) Stop.
2) Don't touch.
3) Leave the area.
4) Tell a responsible adult.
Simple. Clear. Effective.
They have lots of materials to help convey the message (e.g. comic books, etc.).
If you do go with the above, make sure the boy is ready to keep a secret. You do not necessarily want friends, parents of friends, teachers, school nurses, school administrators etc. knowing that there is a gun the home.