<qa>  What is an important risk factor for cognitive impairment?The role of surgical stress and anesthesia is unknown in the early childhood. In vitro and animal studies showed a risk for treatment with anesthesia in the developmental brain. Furthermore, stress is also an important risk factor for cognitive impairment. Therefore, the investigators want to investigate in a clinical prospective cohort study the role anesthesia and surgery on different cognitive parameters and self-controling mechanisms in children under 3 years. 