This study developed, delivered and evaluated an interactive intervention, which targeted three- and four-year-old children's oral language. The intervention was carried out over twice-weekly sessions, for ten weeks. The first weekly session was a group shared storybook reading session with a puppet and the second weekly session consisted of planning, acting out and reviewing a planned pretend play episode based on the storybook, which was read in that week's first session. Ninety-four children were randomly assigned to a control or treatment group and were tested at pre- and post-test on a battery of vocabulary and narrative assessments. The results of a Randomised Controlled Trial showed a statistically significant effect on the receptive vocabulary and productive vocabulary of the children in the treatment group, with medium to large effect sizes. A further positive effect concerned the Mean Length of Utterance (MLU) of the children in the treatment group.