Note that improper breathing can start as an infant.
Poor low tongue posture develops as a result of mouth breathing, along with a tall vaulted palate.
Refer to the article of Mouth Breathing and it's Ill Effects:
International Journal of Pediatric Otorhinolaryngology 75 (2011) 1260–1264
Deleterious sucking habits and atypical swallowing in children with otitis media
Giovanni Ralli a, Giovanni Ruoppolo a, Renzo Mora b,*, Luca Guastini b