lump on sons neck?

Hannah • Hey my name is Hannah. I am a 27 yo SAHM 💙👶🏻 💙4/29/16 💙👶🏻 💙4/23/18
My son has this large lump on the left side of his neck. When he turns his head you can see the bulge. I only noticed it this week and we are going to the peditrician today. Has anyone else seen something similar on their baby's neck and have them be fine. I'm worried.