This dataset comprises the transcripts of participants' speech of the so called `Rejection experiment'. The experiment was designed to investigate the developmental origin of linguistic negation. Participants' speech is directed at the humanoid robot iCub, called "Deechee", and participants were encouraged to adopt the register of child-directed speech (CDS). The data set consists of 50 transcripts based on ten participants and five sessions per participant. Participants are only disguishable by their participant ID. Each participant completed 5 sessions of approximately 5 minutes each.