My twelve year old wanted to try backpacking, but not hike too far. My wife didn't want us to get eaten by bears. The solution? Obstruction Pass!
The hike is short, the campsites are good, and there is a pit toilet, unlike some other backpacking options.
Also the views are priceless. Oh, and there are a bunch of fallen trees that are fun to walk on and see how far you can get before losing your balance.
The hike in is fairly flat, with just moderate ups and downs. The trail also does a loop, which is fun to explore.
My recommendation is to check for burn bans (so you know if you should bring fire wood) and arrive early as these sites are first come first serve.