https://www.cnet.com/news/jodie-foster-black-mirror-arkangel-netflix/

In the clip, Rosemarie DeWitt is the mom who briefly loses her daughter Sarah, but quickly finds her safely. But apparently the incident scares her enough that she signs Sarah up for some kind of medical program to ensure that doesn't happen again. We see Sarah calmly being injected with something uncomfortably near her eyes. (A brain-tracking chip? A kind of Tile for humans? Find my iKid?) 

Not much else is revealed except what might be the tracking company's eerie slogan: "The key to good parenting is control." But in "Black Mirror," technology always comes at a price.