 Data are collected from both parents and children. Measures of key targeted child behaviours i.e., vocal responsivity and initiations and shared positive emotion are coded from videos of child-parent play interactions recorded in the family home on 3 separate days at each of 3 time points: 1 study entry Baseline pre-Training, 2 Post-Training Week 12 and 3 Follow-up Week 24. For each time point, data coded from the videos of child-parent interactions are averaged across 2 days to increase the probability that they are representative of the key child targets and parent variables under study i.e., that they do not represent either a particularly good or bad day. 