This article uses administrative data to explore benefit dynamics for children in Britain's second largest city, Birmingham, over the period January 1998 to June 1999. As the benefits in question (housing benefit and council tax benefit) are means tested, the dynamics are also informative about moves in and out of low income. The article is original in its use of quarterly data to provide a comprehensive picture of benefit dynamics, in treating the child rather than the benefit claimant as the unit of analysis, and also in including ethnic group differences in its analysis of benefit exit and re-entry. It provides a picture of substantial ‘welfare dynamics’: that is, movements in and out of benefit support. Living in a low-income family in receipt of benefit can be seen to be a part, and sometimes a recurring part, of the experience of a large proportion of children. It argues that policy needs to investigate and take account of the impact of insecure income as well as poverty when considering the welfare of children.