the .45/70 guide gun is about the most perfect short/close range defensive dangerous game combo ever made, especially with the garrett ammo, imho. it's fast, with some practice, you can have a 2nd follow up right behind the first as soon as it's coming out of recoil, which makes it nearly as quick as a double, but with a couple more up the spout, anyway, in that situation, you sound like you need an expanding bullet to minimize penetration with that many kiddos around.
another option, i love this for big hogs in texas, and would work awesome in the scenario you bring up, is a puma 92 in .454 casull with some 300 grain hornady xtp's. it's even smaller and quicker than a guide gun imho, and wouldn't overpenetrate and the xtps will open up a wound channel in the thin skinned blackbear something fierce. it will definitely knock the snot out of a black bear.