What does it mean if my 5yr old son woke up with ping pong size swollen lymph nodes on both sides of his neck?

Lymphadenopathy: Very non-specific could be related to any type of infection you should have your son examined by his pediatrician for additional testing and advice.

50/50 strep or viral: Very large anterior cervical lymph nodes are seen particularly in strep throat. A fever would almost certainly be going along with that. You can also see very large lymph nodes with mononucleosis and other viruses so in itself is just a warning sign to keep a close eye probably get a doctor to look at him and do a throat culture.