Brief Answer:
Number of possibilities to consider

Detailed Answer:
Thanks for asking on HealthcareMagic.

I have gone through the description and have checked the attached images. Two broad possibilities come to my mind.
* Simple allergic reaction - Likely to be itchy.
* Eczema - Itchiness is likely to be associated.
* Slapped cheek syndrome, sometimes also called fifth disease - A mild to moderately contagious viral infection common among school children.

I would insist you to take him to a doctor who could confirm the cause and whether rubella or scarlet fever needs to be considered.

Regards

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