Old Robe: Not in Good Shape, but fun!
I too my Girls up on a family favorite hike, Old Robe Trail, that drops down to a gorge where the old Monte Cristo Railroad needed tunnels to get though the walled canyon. The trail hasn't changed a whole lot since hiking it as a kid. They have added multiple switchbacks on the only hill portion of the hike; these make it a lot easier climb and descent.
There is a major slide area, just before the first tunnel (technically tunnel #6). This slide makes what was a fun family hike into a very dangerous, precarious scramble. My girls made it through, but it wasn't very safe and everyone was slogging through it. There really needs to be warning signs at the trailhead.
Reggie, three years old, hiked the whole way for her second week in a row! The river is very fun to listen to and watch. In fact, there were a couple kayakers navigating the rough waters as we arrived at the tunnel.
The girls loved the tunnel and the evidence that there was once a railroad was fun to talk about. This canyon was always a hard spot for the railroad when it was operational in the early 1900's. Slides like the one that is currently there and tunnels collapsing, made for constant clean-up.
I will be editing my description of this hike and recommending that families with small children don't go past the first river spot. Please be very careful if you do plan on making it to the tunnels!