Please don't give them outside food. Best is to cook everything at home for them. Avoid sour foods as well.
One medication which you can use is Himalaya's Amalaki. I tried it myself and I haven't caught any cold and cough in 6 months.
Hot water with lemon juice honey and pepper... helps during colds. . And also helps to keep away. It's yummy too so. ..
Ayushi Ji, those are capsules to be taken in orally. 2 times a day. Ayurveda has no side effects!