it is normal for young children to lose their appetites and eat less when they are sick. you want to keep him hydrated with adequate fluids including water milk broth and popsicles while continuing to offer him food. if this decrease in food intake lasts even when he seems to be getting better or his fluid intake is also low then its best to visit his pediatrician. for more on dealing with sickness see this webmd article.
my 22 month will not eat anything and we offer a variety. he has been sick getting over a cold but will not eat