I personally would be going straight to an urgent treatment center with that or phoning 111 x
They look like hives allergic reaction maybe x
Is he ok? The red on his arms make me think something other than chicken pox! Maybe allergies as others have said! Hope he got checked and is doing better now! X
I’m not sure I’d ring 111. Are they all over his body? Are they on his hands and feet cause HFM is rife atm too.