The ability to interpret others’ emotions is a critical skill for children’s socioemotional functioning. While research has emphasized facial emotion expressions, children are also constantly required to interpret vocal emotion expressed at or around them by individuals who are both familiar and unfamiliar to them. The present study examined how speaker familiarity, specific emotions, and the acoustic properties that comprise affective prosody influenced children’s interpretations of emotional intensity. Participants were 51 7- and 8-year-olds presented with speech stimuli spoken in happy, angry, sad, and non-emotional prosodies by both the child’s mother and another child’s mother, unfamiliar to the target child. Analyses indicated that children rated their own mothers as more intensely emotional compared to the unfamiliar mothers, and that this effect was specific to angry and happy prosodies. Further, the acoustic properties predicted children’s emotional intensity ratings in different patterns for each emotion. The results are discussed in terms of the significance of the mother’s voice in children’s development of emotional understanding.