Schools have added lessons in flu prevention as students packed into classrooms and close quarters spread their germs. Even Elmo and a host of doctors and officials are touting the benefits of proper hand washing. For parents looking for some support in their health and hygiene lessons, several books break the situation down to preschool and toddler levels. The new Felicity Floo Visits the Zoo ($11) tells the tale of a little girl who infects all of the animals in the zoo with a virus when she wipes her runny nose with her hand instead of a tissue. The silly tale reinforces current personal hygiene practices without preaching to its audience. For additional literary picks, check out our selections.