Abstract This study investigated emotion transmission among peers during middle childhood. Participants included 202 children (111 males; race: 58% African American, 20% European American, 16% Mixed race, 1% Asian American, and 5% Other; ethnicity: 23% Latino(a) and 77% Not Latino(a); M income = $42,183, SDincome = $43,889; M age = 9.49; English-speaking; from urban and suburban areas of a mid-Atlantic state in the United States). Groups of four same-sex children interacted in round-robin dyads in 5-min tasks during 2015–2017. Emotions (happy, sad, angry, anxious, and neutral) were coded and represented as percentages of 30-s intervals. Analyses assessed whether children's emotion expression in one interval predicted change in partners' emotion expression in the next interval. Findings suggested: (a) escalation of positive and negative emotion [children's positive (negative) emotion predicts an increase in partners' positive (negative) emotion], and (b) de-escalation of positive and negative emotion (children's neutral emotion predicts a decrease in partners' positive or negative emotion). Importantly, de-escalation involved children's display of neutral emotion and not oppositely valenced emotion.