This winter when gastro went through my son's school, they issued a 48 hour symptom free period. I think if it is a relaly bad outbreak, 48 hours is reasonable. And even after that you have to be relaly careful with diapering...it is carried in the feces so even a tiny amount on your hand or on a surface can infect the others. I would use dispoable gloves for diaper changes for a couple of weeks just to be safe and disinfect the diaper area and bathroom several times a day.