Background: Because the healthcare sector is shifting to a customer-oriented approach, it is important to understand experiences of children as users of healthcare services. So far, studies that measure the influence of medical clowning on patient experiences are scarce. This study aims to measure experiences of children and their parents during day-surgery in hospital setting. Methods: A case-control study was conducted in a large Finnish children's hospital. Seventy children aged 4-17 years coming for a minor operative procedure including pre-operative cannula insertion prior to surgery were included. Thirty-eight children were exposed to the medical clowning intervention and 32 children (the reference group) did not receive exposure to medical clowning. A novel digital survey tool was used to measure patient experiences before and after the insertion of a venous cannula needed for anaesthesia. The children were asked about their emotions, anxiety levels, the pain from the cannula insertion and the best and worst things about the hospital. The parents were asked about their emotions, expectations and the fluency of the procedure and the hospital day. Results: Before the procedure, 32% or 36% of the children in the intervention group and 44% or 28% of those in the reference group expressed positive or neutral emotions, respectively. After the procedure, 76% or 63% of children in the intervention group or reference group, respectively, expressed positive emotions. The intervention group rated the medical clowns as the best aspect of the hospital day. Both groups reported that the best aspects of the hospital day were related to the nurses and food and the worst were related to waiting and pain. Most commonly the parents felt uncertainty, anxiety or calmness before the procedure and relief afterwards. Their expectations towards the procedure related to its success and the certainty of the diagnosis. Conclusions: The results show a trend towards more positive emotions in children with exposure to medical clowning. The digital survey tool was suitable for gathering information about the experiences of children and their parents. Information on emotions and expectations of children and parents during a procedure is useful when improving the quality of healthcare services.