Mertyl is possibly making an error in regards to her belief about the parents in this situation called the fundamental attribution error. The fundamental attribution error is the tendency to attribute others' behavior to internal characteristics (such as personality or disposition) rather than external factors (such as the situation or environment). In this case, Mertyl is assuming that the parents of the crying child are bad parents based solely on the child's behavior without considering external factors that may be contributing to the child's behavior, such as fatigue, hunger, or discomfort during the flight.
Mertyl may be making this error because she is only focusing on the behavior of the child and not considering any external factors that may be influencing the child's behavior. Additionally, Mertyl may be experiencing frustration or annoyance due to the noise and disruption caused by the child, leading her to make a quick judgment about the parents.
To avoid this error, Mertyl could consider other possible explanations for the child's behavior, such as the child being tired or uncomfortable during the flight. Additionally, Mertyl could practice empathy and understanding towards the parents, recognizing that parenting can be challenging and that the parents may be doing their best to calm the child.