Background Parental language is associated with children's later language development. Parenting programmes, based on social learning theory, enhance a range of parenting behaviours, yet there is limited evidence for their effect on parental language. Aim To assess the benefits of a behavioural‐based parenting programme, which features components of language and communication, to enhance parental language. Method Parents of toddlers, aged 12 to 36 months, were recruited from eight Flying Start early intervention centres across Wales. Participants were randomised 2:1 either to a parenting programme (n = 60) or to a wait‐list control group (n = 29). Researchers were blind to participant allocation throughout the trial. Fifteen‐minute video‐recorded observations of parents and children interacting during free‐play, both at a pre‐intervention and at 6‐month follow‐up, provided the data for the study. Five observed measures of parental language were assessed; quantity and variety, encouraging, critical, child‐led and parent led interactions. Intervention The Incredible Years Parent–Toddler Programme (IYPTP) is a 12‐week group‐based behavioural intervention that teaches effective relationship and behavioural management skills including social, emotional and persistence coaching to enable parents to better support their children's development. Results Of 89 dyads that completed pre‐intervention assessments 81 (54 intervention and 27 control) met the criteria for the current study. Intention to treat analysis indicated that child‐led language interactions significantly benefited from the intervention [regression coefficient (B) = −1.44, 95% confidence intervals (CI) = −2.59 to −0.29, P = 0.015, effect size (ES) = 0.47] and a positive trend for encouraging language in favour of the intervention sample was evident. Per‐protocol sample analysis replicated these findings with encouraging language reaching statistical significance (B = 1.07, 95% CI = 0.11 to 2.03, P = 0.03, ES = 0.52). No further benefits were evident. Conclusions The IYPTP has limited evidence as an effective programme for enhancing some aspects of parental language.