Providing helpline services to children via texting (i.e. Short Message Service or SMS) is being used increasingly. However, little is known about the quality of SMS counselling and its effect on the service users. Through a quantitative content analysis of 448 SMS sessions at the Danish child helpline, we studied counsellor behaviour and session impact. We found higher levels of children's well-being and empowerment after contacting the service. Multiple regression models showed that a positive impact of counselling was related to higher density of child-centred counsellor behaviour and moderate levels of problem-centred counsellor behaviour. These findings were consistent across most stressors with positive effects in the small-to-medium range. SMS counselling shows potential as a tool for counselling children and youth.