hi.welcome to healthcaremagic forum. i think your son and daughter are suffering from infectious mononucleosis
and resulted into spleen
enlargement. enlarged spleen is prone to trauma and may get ruptured and may cause even death in worse possible condition.you should avoid any activity which may endanger spleen.regression of spleen enlargement possible.so keep in touch with your doctor and follow their advice.till then do not allow any such activity, at least not against medical advice
. good luck.