My 4 Y/o Son Has A Pea Sized Lump Along

My 4 y/o son has a pea sized lump along his jaw line. It moves side to side. Noticed it today, not sure how long he's had it. Denies pain. Hasn't been diagnosed with asthma but has to use albuterol inhalers 2-3 times per yr. when he was a few months old I was told he has Reactive Airway Disease. What can this be?