Trismus is a rare presentation affecting neonates, children, and adults. In newborns there are serious implications, with potential to affect feeding, cause airway problems, and make intubation difficult. Causes of trismus seen in the paediatric patient are discussed in this review article; they are divided into intra‐ and extra‐articular types. The extra‐articular group consists of congenital and acquired disorders. The acquired group includes infective causes such as tetanus, iatrogenic causes related to drugs, cancer or dental treatment, and trauma causing articulation difficulty or triggering a rare type of bone growth in myositis ossificans. Changes in the mouth resulting from oral submucous fibrosis can undergo malignant transformation. This review aims to raise awareness of potential causes of trismus in paediatric populations, helping clinicians identify the underlying pathology so appropriate strategies for treatment be applied, with the ultimate aim of improving long‐term outlook and quality of life for affected children.