Born in Bradford Age of Wonder cohort: A protocol for qualitative longitudinal research.

Bradford is multi-ethnic and one of the most deprived districts in the United Kingdom where around a quarter of children live in low-income families. Born in Bradford (BiB) has followed the lives of 13,776 children born in the district between 2007 and 2011. Children in the birth cohort are now entering adolescence, and the next phase of the research - Age of Wonder (AoW) - will be a whole city cohort capturing the experiences of 30,000 adolescents progressing into young adulthood.