Take them camping first with sleeping bags and tents. They will always appreciate the trailer much more after that.
Be mindful of the things on the ground, like hot coals, rocks, sharp things left over from inconsiderate previous campers, and hot grills.
Mine are older, and were when we first got the trailer, but even then we liked to pick destination campgrounds where there was something more for them to do there, or something else for us to do in the area. And we have a whole set of different games, ring toss, bean bag toss, ladder ball, frisbee, football, etc to help with the entertainment as well.