The aim of the present study was to examine the contextual effects of social games on prelinguistic vocalizations. The two main goals were to (1) investigate the functions of vocalizations as symptoms of affective arousal and symbols of social understanding, and (2) explore form–function (de)coupling relations between vocalization types and game contexts. Seventy-one six-month-olds and sixty-four twelve-month-olds played with their mothers in normal and perturbed tickle and peek-a-boo games. The effects of infant age, game, game climax, and game perturbation on the frequency and types of infant vocalizations were examined. Results showed twelve-month-olds vocalized more mature canonical syllables during peek-a-boo and more primitive quasi-resonant nuclei during tickle than six-month-olds. Six- and twelve-month-olds increased their vocalizations from the set-up to climax during peek-a-boo, but they did not show such an increase during tickle. Findings support the symptom function of prelinguistic vocalizations reflecting affective arousal and the prevalence of form–function decoupling during the first year of life.