As inevitable a part of motherhood as guilt and fatigue seems to be the goofy addition of "ie" to many words in my vocabulary.
There's the obvious "pee-pee" and "poopie," but other bodily functions also lend themselves well to this derivation. We've got "boogies" and "stuffies" (boogies being the substance itself and stuffies being the ailment) as well as "schmutzies," AKA eye gunk. "Burpies" are the cure for "gassies," while "fussies" are a common ailment for which there is no known cure.
At least we haven't stooped to rhyming every word and starting it with a "w," as in "footsy-wootsy." And spit-up will always just be spit-up.