While the theory about pain in kids was certainly wrong, you are lacking some context about what 'safe' used to mean, and what it means nowadays. In the 80's, kids were under halothane and long-acting paralysis drugs which, especially in cardiac patients, are really dangerous. Halothane is now discontinued, as are many other common drugs from this time. Theories do not spring out in isolation. The evolution of technology, biological understanding and new pharmacology have all contributed to allow new opinions as incremental changes made old theories more and more evidently obsolete. Doctors 50 years from now will also wonder how we could be so stupid in 2025.