But I suspect the true reason parents get kids to methodically collect, catalog, and search out things is that it's supposed to teach them something. Like being an anal retentive obsessive-compulsive has no redeeming social value. People collect the strangest things. Just go to any antique show or flea market and you'll see people who collect salt and pepper shakers, thimbles, spoons with enamel images of the Corn Palace on the handle, Zippo lighters, and strange looks from those of us who don't even have silverware that matches. My dryer lint collection is starting to feel downright normal.
Animals are a popular collecting motif.
Unicorns, pigs, and mushrooms are common. Cows are big right now, probably because people think having cheap plaster bookends that look like Black Angus cows doing a Nixon imitation will give them an alibi when the Got Milk police break down their door looking for people with dark colored moustaches. For a while I collected pink flamingos. Actually, collected is the wrong word. Amassed by proxy would be more like it.