Two siblings, 5-year-old Emmanuel and 3-year-old Cassandra, are brought to your emergency department (ED) in July 2014 by their parents. Both children are up to date on their immunizations and have not had significant medical problems in the past. They were referred to you by their pediatrician for 1 day of high fevers, rash, and pain in the extremities. Emmanuel had 1 episode of gum bleeding last night. His sister has been unwilling to walk since this morning.