Children in the 21st century are avid users of technology--more so than generations past. This rise in use has led to much attention on the consequences of technology use, and how this impacts children's brains and their socio-emotional, cognitive and physical development. Much of the research in these fields, especially brain-based research, is in its infancy. Furthermore, it often shows very small correlations between technology use and child outcomes; whether technology causes these outcomes is unclear, and small effect sizes bring questions about real-life implications for children. Despite these issues, policy-makers in various countries have set guidelines for technology use in children, which are often restriction-focused. This paper explores some of the literature on the effects of technology use on children in terms of their brain, cognitive, socio-emotional and physical development, and summarises what is clearly demonstrated in the literature. It also highlights where more quality research is needed to better understand the impact of technology on children, and support the development of effective, evidence-based guidelines.