Status Updates From Jaws: The Story of a Hidden...

Buteyko Breathing technique is useful to correct oral form at a young age:
Mouth tape, counting steps while not breathing and increasing over time, unclogging nose when clogged will help

Keep your mouth sealed while walking and get to 5 minutes then incorporate in physical activity.

Smile in the mirror for 30 seconds a day to strengthen facial muscles

Breastfeeding is an important part of developing jaw strength. Keeping environments too clean may expedite development of allergies in children and cause mouth breathing which could lead to changes in jaw development and other health effects