Surgical operations, although necessary for the patient's life and health, are frightening and upsetting. The adult recovers from this emotional upset in a reasonably short time and does not necessarily show in his later emotional reactions the effects of the operation. This is not so true of the child. His emotional development, that is, his capacity to handle his emotional reactions, is still incomplete. His ego has not acquired a very stable ability to test reality. His knowledge of his own physiology and anatomy is meager and is confused with weird speculations about the inside of his body, and he is reticent about discussing these weird ideas with adults lest he be laughed at, as has happened so often.
When he has to have an operation, he is seldom told what is going to happen to him and may even not be told that there is to be an operation
PEARSON GHJ. EFFECT OF OPERATIVE PROCEDURES ON THE EMOTIONAL LIFE OF THE CHILD. Am J Dis Child. 1941;62(4):716-729. doi:10.1001/archpedi.1941.02000160017003