 1 It is predicted that, relative to controls, toddlers in the Social ABCs experimental treatment group will show greater post-training and follow-up changes in functional speech i.e., responsivity and initiations and positive emotion sharing with their caregiver. Secondary Aim: It is predicted that 1 parents in the treatment group will achieve fidelity of implementation, and 2 the experimental group will also show greater gains than the control group on standardized measures of receptive and expressive language. Exploratory Aims: Investigators predict that 1 post-training and follow-up child gains in shared positive emotion will be related to high levels of parental facial positive emotion, 2 post-training and follow-up child gains in functional vocalizations will be a moderated by better receptive language at baseline, and b related, in the experimental group, to parents fidelity of PRT implementation post-training. 