The range of techniques available to assess respiratory muscles weakness has greatly expanded over recent years. Respiratory muscle tests can be divided into non-invasive tests, such as lung function parameters, maximal static pressures and sniff nasal pressure and invasive tests, such as transdiaphragmatic pressures during crying, maximal static pressures and magnetic stimulation of the phrenic nerves. Sniff nasal pressure and magnetic stimulation should have increasing relevance in children in the coming years. However, probably the most important message is to arrange for the evaluation of respiratory muscles in children with unexplained or disproportionate breathlessness such as in patients with neuromuscular diseases. Improvements are needed to evaluate respiratory muscle endurance in children, which is more difficult but complementary to the assessment of respiratory muscle strength.