First, shoot a few different things. By that, I mean revolvers, semi autos, shotguns, rifles, anything you can get your hands on. Each person handles recoil differently. Personally, I say a small to medium caliber like the .38 or .9 mm are sufficient for handguns. A .357 will fire the .38 rounds and kick less. I have known girls that were 115 lbs that like shooting huge guns, like .357 mags, .44 mags, etc... but me at 195 lbs doesn't like to shoot anything bigger than my .38 sp.
Second, find a gun that you are accurate with. You have to be deadly with it, not just I can hit paper at 5 yards, but I can take the hair off of a fly's butt at 5 yards. If you need the firearm for self defense, you will need to put a lot of lead down range to prepare for it. You can't just buy a gun that is comfortable and never practice with it. Get to know the gun and how it shoots, what brand/load it likes etc.
Third comment is be ready to accept that using your firearm in self defense means killing someone. Self defense with a firearm is not about disabling. Many of us on this board that have self defense arms have made a concious choice that we can and will take whatever steps needed. Not everyone can do that.
If you are ever in VA, give me a PM and I will introduce you to atleast the .32 H&R magnum, .38 SP, and 9mm. I can also introduce to you a 12 GA shotgun if you want, but I don't travel with my arms so you have to come here to play
When you get your firearm, keep it locked so that your children can't get to it but you can. When they are mature enough (your call at what age, which is why I didn't say older), teach your children how to handle the gun properly and safely. A proper education can save lives, a lesson I learned the hard way. My aquaintance from school was shot 1 time with an "unloaded" .22 . If he had been following the rules for safe handling, he'd still be around and pissing me off.