I came on to the child health topic to ask this exact question!
Last Wednesday evening I noticed that ds (3.5) had a large lump on the left hand side of his neck, thankfully dd had her jabs the following morning so I asked dh to take ds to the dr with him and ask, the dr said it could be caused by nits/lice or a bump to the head, or an infection. We checked for lice etc, nothing, I don't think he bumped his head though he has had a cough and mild conjunctivitis for a few weeks.
The dr prescribed an antibiotic and asked us to bring him in again on Friday of this week.
I've been scaring the crap out of myself googling (don't do that), and trawling through mn history to find any similar threads, but I'm beside myself with worry.
It's hard and immobile though seems symmetrical. And tbh ds wont really let you poke at it so it might be mobile.
Any advice would be greatly appreciated, embolo I know what you mean, I keep looking at it then panicking , I'm actually scared to touch it as I'm a head in the sand kind of person!