is tnis wrong of us?

if gastro virus (tummy bug) is going through my step kids mothers house right now is it wrong for us to keep them here with us until its ALL GONE (Could be 2 weeks). One child has been struck down with it, if another or his mother catches it.... we would rather the step kids are away from all that till its all gone. i have an infant at home and a 2 year old as well as a 6yo and 8yo ... i dont want my kids catching it. so what would you put first? the health and wellbeing of your step kids and bio kids (keep them away until its all gone) or take the risk and let them go back to their mothers regardles if people are sick or not.