My 5 year old has been caching with me since she was 4. Hey, that's 20% of her life.
At first she was happy to follow the arrow.
Now she uses the WP code I tell her, goes through the closest menu, finds the waypoint, sets the goto and we're off.
On occassion when the WP is not on the closest list, she will go back to the full list and scroll down to fin dthe WP. Then it's to the goto and we're off.
We haven't gotten to the point where she enters WP's manually (on a multi) but I expect that time is not far away.
We also use this as a reinforcement of her alphabet learnings at school.
eg. GCK000 and GCN000. Which one would come first in the list, should she scroll up or down.
It's fun for her and as she gets more dextrous with the fingers, we'll be onto manual WP's sooner rather than later.