In fairness to the mother, it's relatively common for children who go missing to be found hiding somewhere nearby (common enough for the police to be aware that they need to search around the house and garden). Apparently they get scared to come out, especially when they hear all the fuss. So it's not really that strange a story, other than that the press covered it.
I would notice right away if one of my children didn't make it to school, because there are only two of them. If I had eight I can easily see how one might slide by under the radar on a busy morning.
Glad everything was fine.