Making poopies refers to the act of taking a dump or taking a shit. This is the process of emitting fecal matter out of one's posterior orifice. I don't know why the term: 'taking a shit' caught on, since you're actually 'leaving' a shit'. Making poopies can be a means of describing your current situation or that of someone or something else. This expression can be used in differing tense's as given in the examples below.
Honey, you're not gonna believe this, but I have to make poopies.
Hey Louie, where's the poker dealer? Oh, he's in the shitter out back making poopies
The act of sneaking into someone else's room, dropping a payload in their toilet, not flushing, and then leaving a note signed 'Pooping Tom' on the toilet seat. Usually occurs in college residence halls.
"Dude, someone left a big, steaming pile of feces in my toilet with a note that said 'Courtesy of the Pooping Tom'!"
I've gotta stop eating those damn peppers before I bonk my babe. Tried to slip out a silent one during the hot action and out came some loose poopies. She was pissed but laughed anyway. Made me sleep on the couch.
Lil Timmy and his annoying lil friends wanted to play football on the grass field in the local park. But they soon discovered that the field was filled with dog poopii.