Hello Madam,
Dnt worry for this. All you have to do is keep 100 % attention to the brushing and cleaning of teeth of your child every time he is having any sugary food. Make a habit of brushing during night. If you dnt take care now he will lose all his milk teeth and might create problems for the permanent teeth.
Pls follow up proper brushing and mouth rinsing.
Next Steps
You can visit any Pedodontist and get filling done for the caries. You can ask the pedodontist regarding how to take care of the oral hygiene and what tooth paste can be used for your child.
Health Tips
Better you visit a doctor soon and get the fillings or necessary treatment done. Then maintaining the oral health will be easier.