Care and Feeding Photo illustration by Slate. Photo by Anton Zacon/Getty Images Plus.  Care and Feeding is Slate’s parenting advice column.  Have a question for Care and Feeding?  Submit it here . Dear Care and Feeding, My boyfriend, “Dexter,” has a 2-year-old nephew, “Mark,” that he watches for his sister twice a week while she works. The other day, when Mark was over, Dexter served him something that looked suspiciously like dog food. When I later made a joke about it, I was horrified to learn it was the genuine article! In response to my demand as to why the hell he would give his nephew dog food, his reply was that Mark had gotten into the dog’s food one day and really liked it. Dexter said Mark is typically a picky eater, but he goes for the dog food every time, and it’s easier than dealing with a meltdown from him. I am beyond grossed out here. Is this something that should have me reconsidering my relationship, and do I need to inform Mark’s mom about what her son has been eating?…