Children are rarely affected by medical emergencies. The experience of doctors or paramedics with child emergencies is correspondingly poor. The anatomical features and individual calculations make such an emergency much more error-prone than a comparable adult emergency. Particularly in dose calculations, critical errors occur time and again. Since these calculations are based on the child's weight, which is preclinically often derived from the size of the child, the number of errors can be minimized with an assistance service that performs all calculations based on the size. Technically, it is possible to detect the size with a depth camera, which is occasionally installed in smartphones or head-mounted displays. In order to investigate to what extent these cameras provide precise results, a study with 33 children was carried out. The children were measured with both an emergency ruler and an augmented reality app with associated smartphone with depth camera. The result is that the depth camera does not provide significantly different results than an emergency ruler. This allows further research, e.g. the automatic recognition of patients with the help of machine learning or usability studies, to be tackled.