hi there. ginger root and garlic both have anti-biotic actions. echinachea boosts the immune system. ginseng also has the same effect. apples have an anti-viral effect; eat apples at-least three times a day or alternatively drink a pint of apple juice (even supermarket apple juice should help). take zinc and vitamin C supplements- both are vital for healthy immune function. lavender essential oil has an immuno stimulant and is also an anti-biotic. finallly, specifically for sinusitus (these are essential oils): sinusitis with head pain, use eucalyptus and lavender; with congestion, use basil; with catarrh, use eucalytus and sandalwood.
for your son, try lavender essential oil in a bath 3 drops diluted in 15ml of carrier oil) and then a drop on his pillow.
hopes this helps,