Reliable non-invasive tests that are feasible in early childhood are essential to the study of transmission of Helicobacter pylori, since most individuals get infected during the first years of life. New tests are validated by comparison with a "gold standard", but no single test for detection of H. pylori infection can be used as a fully reliable reference method. Therefore, concordant results of at least two biopsy-based tests (histology, culture, rapid urease test) are considered as the "gold standard". Most of the validation studies in children included only a few infants and toddlers, with low numbers particularly for H. pylori-infected individuals. Only when increasing numbers of patients were tested and separated into subgroups by age it became apparent that the accuracy of most tests is lower in young children if the same cut-off values are used as established for older children or adults. Therefore, statements such as "a test has been validated with good results in children" must be interpreted with caution, unless different age groups are considered with sufficient numbers of infected and non-infected children in each age group.