Background
Atypical speech and language development is one of the most common developmental difficulties in young children. However, which clinical signs characterize atypical speech–language development at what age is not clear.

Aim
To achieve a national and valid consensus on clinical signs and red flags (i.e. most urgent clinical signs) for atypical speech–language development in children from 1 to 6 years of age.

Methods & Procedures
A two‐round Delphi study in the Netherlands with a national expert panel (n = 24) of speech and language therapists was conducted. The panel members responded to web‐based questionnaires addressing clinical signs. Consensus was defined as ≥ 70% of the experts agreeing on an issue.

Outcomes & Results
The first round resulted in a list of 161 characteristics of atypical speech and language development. The second round led to agreement on 124 clinical signs and 34 red flags.

Conclusions & Implications
Dutch national consensus concerns 17–23 clinical signs per age year for the description of an atypical speech–language development in young children and three to 10 characteristics per age year being red flags for atypical speech–language development. This consensus contributes to early identification and diagnosis of children with atypical speech–language development, awareness and research.