After trying (and failing) to set up a night course last year at Crooked River, I made a second attempt. This night course spans 10 fire tacks and is roughly 500 meters of walking (at the shortest distances). The course never goes outside the boundaries of the park, and you will never have to enter another person's campsite.
To do this night course, find a GOOD flashlight. Note that a flashlight that is too weak, or cannot have the beam narrowed, will not be able to spot one tack from the previous one. For this course, you should be able to always spot the next tack while touching the tree with the current tack you are on.
Another tip - hold the flashlight at eye level. Fire tacks reflect light directly back along the path of the light beam, so you want the light beam held at your eye. Holding the flashlight at your waist will not work.
The fire tacks used for this course are a white square style. The final location has three fire tacks in a vertical line, and the cache is hidden just on the far side of the tree with these tacks.
Always remember - you will be in the woods at night, so practice bear awareness. This is intended to be a short, beginner course, so it is suitable to bring children. Hopefully it will help your little campers not be afraid of the dark. :-)