Of a sample of 1,616 children aged 3-6 years, 38% required orthodontic treatment and 46% had signs of crooked teeth.
The prevalence of mouth breathing and poor sucking habits were closely related to anterior open bite, posterior crossbite and increased overjet (abnormal alignment of the teeth/crooked teeth).
Children can practise simple breathing exercises to help decongest their nose, and change to nose breathing. See Patrick McKeown’s free online training for children.
Paolantonio EG, Ludovici N, Saccomanno S, La Torre G, Grippaudo C. Association between oral habits, mouth breathing and malocclusion in Italian preschoolers. Eur J Paediatr Dent. 2019 Sep;20(3):204-208. https://pubmed.ncbi.nlm.nih.gov/31489819/