A rapidly spreading rash in a child, especially without fever or systemic symptoms, could suggest viral exanthem, allergic urticaria, or mild dermatitis.
Since your child is active and otherwise well, it is likely benign but needs monitoring.
Next Steps
Continue calamine lotion to soothe the skin.
Antihistamine syrup (as prescribed) will help control spreading if it’s allergic.
If rash worsens (becomes red, painful, or develops blisters), reconsult a pediatrician/dermatologist urgently.
Health Tips
Avoid using any new soaps, lotions, or detergents. Keep your child’s nails short to prevent scratching and secondary infection. Most viral or allergic rashes settle within 7–10 days.