Ideas
I am also having this issue. Today is the first time. I got a notification that one of my children would be taken away due to low grades, but she's an A student, so i thought it would be fine. Just in case, I made sure she was doing her homework and projects every day. A couple days after that notification, she was just randomly taken. She had full needs, is an A student and nearly full relationship with both parents. I also got the life and death ghost popup.
I am using mods, but i turned off mods, and it still happened. I did add a few new mods today, but I don't think that's the issue, as it still happened when they were turned off.
I do not want to age them up to teen because that would ruin the point of this save. I tried several things, but every time they got taken away around 4:59am, including reset sim (debug), repairing the game, and using a cheat to make sure all needs were 100% full.