Public library makerspaces intend to contribute to the development of children from marginalized communities through the education of digital technology and creativity and by stimulating young people to experience new social roles and develop their identity. Learning in these informal settings puts demands on the organization of the makerspace, the activities, and the support of the children. The present study investigates how children evaluate their activities and experiences in a public library makerspace both in the after-school programs and during school visits. Furthermore, it examines the effectiveness of the training program for the makerspace coaches. The study covers self-evaluations by children (n = 307), and interviews with children (n = 27) and makerspace coaches (n = 11). Children report a lot of experiences concerning creating (maker skills, creativity) and maker mindset (motivation, persistence, confidence). Experiences with collaboration (helping each other) were mentioned to a lesser extent. Critical features of the training program for makerspace coaches were (i) adaptation to the prior knowledge, skills and needs of makerspace coaches, (ii) input of expert maker educators, (iii) emphasis on learning by doing, (iv) room for self-employed learning, and (v) collaboration with colleagues.