signs of childhood leukaemialeukaemia cancer symptomslymphocytic leukaemia symptomslymphoblastic leukaemia symptomschronic leukaemia symptomssymptoms of leukaemia in teenagerleukaemia relapse symptomsmyeloid leukaemia symptomsleukaemia nosebleedssymptoms of leukaemia in elderlyleukaemia petechiaeacute leukaemia symptoms