Background Mental health disorders in children are common. General practitioners (GPs) have a significant role in the detection of these disorders, yet there is lack of evidence to assess this ability. This study aimed to explore GPs' recognition of children's mental health problems, examining GPs' ability to identify both a common emotional and behavioural disorder. Method Between November 2014 and March 2015, an online survey‐based questionnaire measure was used, composed of a series of six clinical vignettes designed to assess GPs' mental health literacy with respect to children of primary school age. This included recognition accuracy, rating of problem severity, and degree of concern about hypothetical cases, described in the vignettes. Results Of the 97 participants, all identified the clinical level separation anxiety disorder and 97.9% identified the clinical level oppositional defiant disorder. Nonparametric analyses identified a significant difference (Z = −5.44, p < .0001, r = .55) in the GPs' concern for the child with clinical oppositional defiant disorder versus the concern for the child with clinical separation anxiety disorder. Participants were significantly more concerned about a boy presenting with clinical separation anxiety (Z = −7.18, p < .001, r = .72) than a girl. Also, participants were significantly more concerned about a boy presenting with clinical level oppositional defiance (Z = −7.79, p < .001, r = .79). Conclusion This study shows the majority of GPs can identify a primary school child with clinical level symptoms of either a common emotional or behavioural disorder described in a written vignette. However, GPs were more concerned when the child was male or displaying symptoms of a behavioural disorder.