It happened when your child for the first time opened their mouth to breath more air. But we also know how to help it. Basically, you should follow the recommendations we gave in 'practical advise' section. Pay attention at your child's lifestyle. Try to organise more time for them to do sport on the open air.
Physical activity is natural for child and brings health.
An the same time restrict their time watching TV, playing computer games etc. because these things damage health and corrupt mind. By all means avoid junk and fast food. The worse things for children are chocolates, popular drinks, all packed chips, sweets etc. Watch your child's mouth. Use procedure we described already or 'steps'.