My son is 5y 6m .He was suffering from sinusitis last week.According to doctor he will have to be keep in care.what type of care will give him?

It is important to treat colds and allergies quickly to avoid a secondary infection developing in the sinuses. Reduce nasal congestion by frequently using a nasal spray.
Use protection mask while traveling.
Drink plenty of extra fluids when you have cold.

Sinusitis is horrible sometimes, I too have. Recently I started applying Patanjali 's Divya Dhara (suggested by one of my friend) and its very effective. Don't apply on his face but apply on his clothes and pillow.

As Revauthi said it comes when he travels with crowd, So make him wear mask.