Almost half of the 3,135 counselling sessions about exam stress were with 12-15 year olds, and 237 were with children aged 11 and under.
The biggest rise was in children aged 16-18, who were taking A-levels to get into university. Counselling sessions for this age group had increased by 21 per cent.
The charity said that children in their early teens were picking up on worries more commonly experienced by university students about getting a job.
They were also more likely to compare themselves with others who were also posting on social media about job searches and exam results, and to worry about the economy after overhearing their parents talking about it.
The job market is increasingly competitive as a record number of students graduate from university with 2:1 degrees and many fail to find graduate-level work.