What's this rash? Photos included

[threelittlesoliders]

So yesterday afternoon I noticed a slight rash on my 3yo cheek. Nothing major, so didn't think much of it. However...
This morning it has come out as shown in the photos, now on both cheeks and on one arm. I've given piraton, which doesn't seem to have made a difference. He states that he feels ok, he has no fever, and it doesn't itch.
He doesn't have eczema, which I first thought he cheeks looked like, but the arm in particular has me stumped.
Any ideas?

Prickly heat?

Reaction to sun cream maybe?

Thanks for the replies..

Hoping it's just prickly heat!

We didn't spend much time outside in the sun yesterday, all activities were inside, so he wasn't wearing sun cream.
Thinking it could possibly be a reaction of some kind though, perhaps he rubbed up against something.