hi thanks for consulting HCM As you said your child grind his teeth in night (bruxism) In children it commonly occurs during or after eruption of baby teeth around age of 3 to 4 years and during permanent teeth eruption that is between 6 to 12 years... sometime its get corrected by itself as child ages.. it could occur due to * irregular contacts or alignment of teeth * stress or anxiety * medical condition like nutrition deficiency worm infestation endocrine disorders * jaw problems As you mentioned he is not taking food properly it may be due to worm infestation but i will advice you to go for thorough checkup by your pediatrician and dentist.. You can give him deworming medicine if needed.. it is given based on body weight of children and type of worm infestation so i would advice to give it only under doctors prescription.. Generally for 3 year old child night guard to protect the teeth is not necessary if condition is not severe.. Give extra attention to your child if it seems psychological especially before he go to bed.. give massage and relax the perioral muscles of child.. Give plenty of water to prevent dehydration.. hope it will help you take care