Hi I know you can't diagnose over the Internet. I'm thinking it's a viral rash as he has a runny nose and slight cough. Just after a little reassurance really. As it looks really really red in person.
No rash anywhere else except behind his ear a little.
He's fine slightly whingey. Woke crying about a sore leg last night but that's the third time in as many months so think that is growing pains. Legs fine in the day.
Thanks