I had to buy some coin cell batteries a few months ago (CR2032s or similar) and was surprised to see the package proclaiming they’d done that. Made sense, but had never thought of the need before.
Coin cell batteries can kill toddlers within 48-72 hours if swallowed. Even if they don't kill, they can cause terrible internal burns when the gut shorts the terminals.
If there is any suspicion of swallowing a coin cell, go direct to hospital. Do not give the child anything to eat or drink until given the all clear.
Kids swallowing coin cell batteries is a recurring and very serious problem. Hospitals will take it very seriously (x-rays, etc) if there's even a suspicion that one has been swallowed.
