This paper explores the implications of children's out-of-school digital multimodal composing practices on learning and teaching in the formal educational context. It adopts a case study approach where publicly accessible "YouTube" video productions of three children around the world are examined. Applying a multimodal discourse analysis approach, we analyse the children's videos and discuss what they suggest about the children's literacies and skills. We argue that children's digital multimodal composing practices demonstrate their creativity, critical thinking, and a semiotic awareness. Following the case studies, we discuss how the educators can respond to students' out-of-school literacy activities by creating the 'third space' for learning in schools.