From the given clinical photograph it seems that, there child has deep caries with molar tooth of upper jaw which is causing pain .
Next Steps
visit dentist / pedodontist for further treatment so as to avoid further damage to the tooth.
Health Tips
-avoid eating sticky foods& give lots of nutritious food like fruits and vegetables regularly to improve immunity & oral health.
-use proper brushing technique with fluoride containing toothpaste in a pea size amount only twice daily on a regular basis to maintain oral hygiene.