Q. A friend told me that Judaism doesn’t allow a child who is a doctor to operate on or give an injection to his or her parents. Is this true?
The rabbis discuss what happens if the child’s action is for the parent’s benefit, e.g. letting blood, which used to be a recognised medical procedure. In theory this is allowed, though there is a preference for it to be done by someone else. The Shulchan Aruch does not permit a child even to remove a splinter from the parent’s hand (YD 241:1), but it is allowed if no-one else is available to do it. A number of rabbinic responsa are lenient especially if the parent asks the child to treat him/her.
There is a psychological aspect to the problem in that the child may be scared to operate on a parent, but if the doctor is an expert at the particular procedure and is the best one available he/she is unlikely to carry out the task inefficiently.