Consider bringing a small plastic "groundcloth" to spread out the cache items for your kids to view.
Picking the right item will often be a big decision for them, and spreading them out will be easier than trying to balance the stuff on that tree stump.
Are you a "mailman cacher" (through rain, snow, sleet or hail)?
If so, remember to bring along something to cover the cache container after you open it (an umbrella, jacket or something) so that no moisture gets into the container.
Sealing a container tightly isn't much good if you've just sealed water into it…