I found this OP which might be helpful:
Enteroviruses (like hand foot and mouth), can sometimes cause mild irritation of small blood vessels in the skin, especially as the rash is healing.
It’s not unusual to see tiny red or purple dots (sometimes petechiae or pinpoint marks) appear as the main rash fades.
These can occur where the skin was most inflamed or rubbed (hands, feet, mouth area, or even limbs).
If the child is otherwise well, active, eating, and afebrile, it’s usually just part of the skin recovery process.
Even though this sounds mild, petechiae always warrant a quick check if:
New spots appear suddenly or increase in number
They are widespread or not limited to areas of rash or friction
The child becomes unwell, drowsy, irritable, pale, or develops a new fever
In those cases, you’d want to have them seen urgently (same day) to rule out rarer but serious causes like meningococcal infection.