Background: With a potentially early onset, hereditary angioedema (HAE) requires special knowledge also in infancy and early childhood. In children from families with HAE, the diagnosis should be confirmed or refuted early, which can be difficult. Studies of childhood HAE and the diagnostic approaches are limited. Our aim was to investigate the entire Danish cohort of children with HAE and non-HAE children of HAE patients for diagnostic approaches and clinical characteristics. Results: We included 41 children: 22 with HAE and 19 non-HAE. Of the HAE children, 14 were symptomatic-median age at onset was 4 [1-11] years. The first attack was peripheral in 8/14 children and abdominal in 6/14 children, i. e. no one had their first attacks in the upper airways. Most children had less than one attack per month. All of the symptomatic children had been treated with tranexamic acid and/or C1 inhibitor concentrate. Unlike in other countries, androgens were not used in our pediatric cohort. Home therapy with C1 inhibitor concentrate was established in 9 cases: 6 children were trained in self-administration and 3 children were treated by parents. Of the children, 10 had been diagnosed by symptoms, including 3 without family history-median age of diagnosis among these children was 5.35 [2-13.2] years. In 31 children, HAE was diagnosed or refuted before symptoms by blood samples. In 23 of these children, complement values were investigated, and in 9 cases genetic testing was added to the complement measurements. In 8 children recently investigated, genetic testing was first choice. Cord blood was used for complement measurements in 9 children and for genetic testing in 4 children. Results of complement measurements were equivocal in several cases, especially in the cord blood samples, and the sensitivity of low complement C4 for the diagnosis of HAE was 75%. Conclusions: We investigated clinical characteristics in all Danish children with HAE. The rate of home therapy was high and androgens had been avoided. Complement values were often equivocal, especially in cord blood samples. Consequently, we have changed diagnostic practice to early genetic testing in children where the family mutation is known.