They have an algorithm which can account for every micro-taste on the planet. What's the point of having computers if they can't properly account for the real world?
Because, for one thing, the purpose of Netflix is to display movies and TV shows. Almost every movie or TV show ever made has some children in it somewhere, at least in the background.
When your entire content is full of triggers for those who lost a child, what's one more trigger at the loading screen?
They just need to add an option to hide the "kids" profile, which, as is being noted all over this comment thread, would be useful for a number of reasons.
They're just sitting down for a relaxing movie or series and the first thing that comes up is the question: "You don't have kids right?"