Why do children catch flu or fever easily? what is the best way to avoid that? thanks

Behavior/vulnerablty: Newborns have passive protection from their mother against many common viruses but this fades by 3-5 months.After that point, they will experience on average 5-7 respiratory and 1-3 diarrheal illnesses/yr to age 5. As the do they build protective antibodies against similar germs. They are also very oral, touching their mouth with contaminated fingers often.Wash hands often, it improves with age.