Some studies report delayed theory of mind (ToM) development in children with specific language impairment (SLI), while others do not. A ToM delay is acknowledged in children with autism spectrum disorder (ASD), while whether these children also display a deficit is still under debate. In the current study, we drew on a developmental trajectory approach to assess whether children with SLI or ASD displayed delays or deficits in their ToM performance. Forty-three children with SLI (age 4-10 years), 44 children with ASD (age 5-12 years), and 227 typically developing children (age 3-11 years) completed the ToM Storybooks. Children with SLI were not found to display either a delay or a deficit in ToM, while children with ASD were found to display a deficit.