With little ones I would park at Old Mans Cave, hike down the steps to see the falls and come back out. It seems like you are walking into prehistoric times with the impressive rock formations. While there they would probably enjoy the suspension bridge that goes across the gorge.
You can see Ash Cave by again parking in the lot and taking a short paved hike back to see it. Small kid will really be in awe as this is the tallest most impressive rock formation that is easy to get into.
Conkles Hollow has an easy hike in and out from the lot on the lower trail. If you are energetic the upper trail is one of my favorites but the kids must be well behaved as there are some pretty big dropoffs.
I would not take kids to Cantwell Cliffs.
Cedar Falls can be a short walk from the lot as well but there are many steps.
If you are staying at the State Park and the kids like to fish, you can walk through the group campground (behind the pool) down the hill to Rose Lake.
There are zip lines in the area and 4 wheeler rental, plenty to do.
You will enjoy the trip.