While many people have heard of mono and associate it with kissing in teenagers, that is not the primary group or way it is spread. The virus is typically spread by close contact with others, such as living in the same household and sharing eating utensils. Though not as contagious as a regular cold, mono occurs very frequently in young children, and many times it appears to be just another viral illness. Children may not have the fatigue that adolescents tend to experience, but they often have high fevers that persist for many days.
Although the virus can be present in the mouth and saliva for months after the acute infection, it's not really possible to determine how long a patient remains contagious. We can't keep a child from playing with other children for months, so the most important thing to do for a child who has recently had mono is to wash hands frequently and to refrain from sharing any kind of eating or hygiene utensil. Children should stay away from a child diagnosed with mono only for the time that the child is feeling ill. Generally, when children have fever and feel fatigued, they should not play with other children. Once the child is feeling better, has returned to his regular energy level, and is on the road to recovery, he can socialize again.