The Oxford English Dictionary is many things: the largest dictionary in the world, an attempt to completely record the English language, and the closest thing we have to word-lover's crack.
One thing it's not is snobbish. To create a full record of English means to delve into all realms of human experience, which parents and lexicographers agree is full of number one, number two, pee-pee, wee-wee, doo-doo, tinkling — and even the occasional poopie-plops. The OED first noticed these terms (with their toilet-y meanings) in some diaper of our literature in the years 1902, 1902, 1923, 1937, 1954, 1965, and 1975 respectively.
"Poopie-plops" — a vivid word for a dump — is the mere tip of the poo-berg, as the OED has plenty o' "poo" and "poop"-related terms, complete with citations to illustrate their collective stain on our language and culture. It's as if the OED took this 1989 quote as mission statement: "If there's one thing I've learnt in the army, it's never to ignore a pooh-pooh!"
—"Pooty" (1825) is a regional variation of "pretty," much like "purty." And yet, nine out of ten women, when described as pooty, file charges.
—The "pooh-pooh theory" — old as 1861 and still discussed — is "the theory that language is a development of natural interjections," meaning "Shall I compare thee to a summer's day?" evolved from "Oww!" and "Aiiiiieeeee!" and "Guh!" I don't know if that theory holds any toilet water, but there sure are a lot of poo-sounding exclamations, such as "Pho!" (1601), "Phoo!" (1672), "Poh!" (1559) and "Pooey!" (1932).
—Here's a child-friendly version of "when the shit hits the fan" that I encourage you to use with your own child immediately: "when the poopy hits the paddles" (2000).
—The sense of poop as information dates from 1911 and has a military origin. A "poop sheet" — in contrast to a poopy sheet — is full of facts, not feces.
—If you're tired of calling your enemies and cousins names such as "poop-butt" (1967) and "poop-head" (1955), why not reach back to the thirties for a fresher insult: "poop-stick."
I'll close with a 1938 citation that upholds the pooh-pooh theory while having a metric diaperload of general truth as well: "In the dawn of language, the bow-wows and the pooh-poohs and even the ding-dongs must have served man well."
Indeed.