Hi A 3 year old, unable to stand on his own is a matter of concern. It is not as simple as calcium deficiency. A detailed assessment of the weight, height, developmental milestones (gross motor/fine motor, speech and language, social) and systemic examination (detailed examination of the musculoskeletal and nervous system) is needed. His vitamin D status should also be looked into. It would be better if you have him seen by a Pediatrician. For the teeth problems, dental hygiene and an appointment with a dentist will be needed. Till then you may give him calcium supplements available in chemist shops. (Shelcal/ Ostocalcium suspensions) Hope my answer helps you. Wish your son good health.