Problems of speech and language in early childhood can influence a child’s emotional development, academic prowess and quality of life. This article is a consensus report from the Netherlands describing 124 clinical signs and 34 red flags of atypical speech and language development, which could help in early identification and intervention in these children. The report describes speech and language development within the linguistic domains of phonology, semantics, morphology, syntax and pragmatics and also in the non-linguistic domain of interaction for six age groups. For example, a child who does not show ‘interaction’ at the age of two years should be suspected of having either a hearing impairment, autism spectrum disorder, intellectual disability or difficulty with language. Further evaluation of the child and diagnosing the aetiology will help to decide whether further intervention is necessary. The authors have contributed significantly to our knowledge on childhood speech language development. Educating parents and teachers about these signs and red flags will be crucial for developing early intervention programs.