The Evaluative Space Model of emotions allows for the coactivation of positive-appetitive and negative-avoidant systems, but few studies have examined mixed emotions in child development. Existing research suggests children’s understanding of opposite valence emotion combinations emerges by approximately 11 years of age. However, it is not yet clear whether various opposite valence combinations are understood at different ages, nor whether children can understand them in others before they have experienced such mixed emotions themselves. Semi-structured interviews with 97 children investigated whether they regarded six combinations of opposite valence mixed emotions as possible, could provide reasons for them, and report their own experience of each in the context of mother-child relationships. Both understanding that such combinations are possible and ability to provide reasons for them increased after age 6 and up to age 11, but were still incomplete in 12-year-olds. Understanding of different opposite valence combinations developed at different rates. At each age, fewer children who showed understanding of these combinations in others reported having had a similar experience themselves. The findings suggest a need to systematically examine a range of mixed emotions in order to develop a comprehensive theory of the development of mixed emotion understanding. They also suggest extending research into adolescence.