It is an agonising death over a period of days/weeks for the child and horrible for the parents to witness. Many times both the parents and medical professionals don't realise what is actually happening to the child until it is too late. There is growing support for much tighter regulations of these batteries and limiting there use overall.
Apple is certainly not the only company who are using them, not by a long shot. But they are not some holy grail of replaceable batteries and it surprising Apple would decide to use them now.
If you are interested ABC in Australia did a rather big report into the increasing incidents of button battery related deaths and injuries, telling the story of families who's lives were turned upside down by them. It is incredibly difficult reading.
https://www.abc.net.au/news/2021-02-15/button-batteries-land...