Answer:
Follow up with both the parent and the child about their experience and how it affected them, then evaluate the likelihood of it happening again and decide whether it's worth continuing with the study.
Step-by-step explanation:
There is no one answer to this question, as it pertains to ethics in research and like most ethical questions, it requires a discussion. While intentionally harming or negatively affecting a participant in a study is never right, we can cause some discomfort if this is an acceptable level, the participant is well informed and knowingly decided to participate anyway, and it will provide us with valuable information for the purposes of the study. If the IRB received a report of a child becoming upset they must investigate the report. They need to know how the child's behavior changed while being upset, did it produce any lasting effects on the child and mother, and if it was due to the study's protocol or to a particular characteristic of the child or mother. With this they can estimate how likely it is for the incident to repeat and how it would affect future participants. Finally they must weigh this against the benefits the study could bring, only continuing the study if the discomfort that could be caused is acceptable and it will provide valuable information.