Improving children’s mental wellbeing is a recognised public health priority, but evidence on recent trends is lacking. This study updates evidence on differences in child mental health since 2008 by comparing two nationally representative cohorts in Wales, UK. Parents of 4- to 12-year-old children completed the Strengths and Difficulties Questionnaire (SDQ). No significant differences were seen for younger girls between 2007/2008 and 2012/2013. There was a decrease in conduct, hyperactivity and total difficulties symptom scores and an increase in prosocial scores for boys and older girls. These findings suggest that rates of child mental health problems are stable or falling.