if you are cycling for more than a few hours, the kid needs OPTIONS.

Tired: sit in a trailer
Not tired: pedal on the trailabike. (Put gear in the trailer.) or tow with a trail-gator-tow-bar
Tow bar also adds the option for the kid to pedal independantly.

Other options: old used tandem w. trailer. (If the kid is big enough to ride stoker.)

The limiting factor might not be the cycling at all--it might be the length of the camping trip--what's the longest he's done?

Having said all that--go for it!!