Most common cause of lymph node swelling is infection by virus, bacteria or fungi in the area which drains into that lymph node. Other causes may be injury, cancer, immunological disorders, lymphomas etc.
General swelling of lymph nodes throughout body may indicate an infection, such as HIV or mononucleosis, or an immune disorder, such as lupus or rheumatoid arthritis
The Smudge cells present in blood may be 0.01% in severe infection of may be up to 20 % in lymphocytic leukemia
High lymphocytes, low neutrophils, and high monocytes counts may be elevated in infectious mononucleosis
, infection, certain bacterial infection like TB, typhoid etc.
As per information provided, you child is probably suffering from viral infection. Ask your doctor for further investigation like lymph node biopsy
(FNAC), PCR for EBV, Widal, PS examination by pathologist, blood culture
etc. to confirm diagnosis.