If you're not going to take the time to really practice, a revolver is your best option. Its just point and pull trigger, if it doesn't go off, pull trigger again until it does. You don't want to have to remember to take a safety off in a bad situation, or how to change a magazine, or clear a misfire. The 5 pound trigger pull makes it very difficult for a child to accidentally shoot. A simple bio metric safe by your nightstand makes it safe and accessible.

My wife has the S&W 5 shot 38 special, with hidden hammer. It's small and lightweight, the recoil is minimal. Its not the largest caliber but it will do the trick if its needed.