Wherever their parent left them unattended, presumably.

My guess was backseat of car. Parent has lab supplies back there, including a few 10-pack boxes of these, which also work as an improvised distraction/toy just like rare earth magnets or monkeys in a barrel. Unfortunately they weren’t checking rear view mirror because work it’s stressful, so kid put quite a few down without their knowledge. They didn’t even notice until day 2 migration to large intestine and rectum. This parent is overworked and under-appreciated and I’m so glad I’m not responsible for children.