If a child has a nasal blockage or has large tonsils, they can’t breathe properly through their nose. This leads them to be a mouth breather. When the breathe through their mouth, the position of the tongue is such that it does not full develop the upper jaw. This leads to a narrow jaw and therefore the teeth do not have any space to come through straight and end up being crooked teeth. https://www.clearbracesorthodontics.com.au/myobrace-no-braces.html