This article explores children's use of digital popular culture as boundary objects, and the transmedial boundary work done in Swedish school-age educare (SAEC) centres. As children bring their experiences of digital media into everyday SAEC practices, they influence, and are influenced by, others around them, children as well as adults. Through field observations conducted in a Swedish SAEC centre in southern Sweden, we collected ethnographic field data, together with two groups of children in Years 2-3 (aged 8-9) and staff. In total, 47 children and 7 staff members took part in the study. Using Star and Griesemer's (1989) theory on boundary objects, we analyse how children's digital popular-cultural interests are brought into, and made relevant to, SAEC practice. The results show that children's use of digital media is transformed in SAEC activities into analogue content -- drawing, dancing, etc. -- and that these activities are ways for children to establish social relations by displaying and sharing their interests. These results have impact for the continued development of extended education, the use of digital media and its value for SAEC, as well as teachers' ongoing practice.