Welcome to HealthcareMagic forum.
Your son most probably seems to have a fungal infection( yeast).
The appropriate treatment usually includes topical antifungal
ointments containing miconazole or terbinafine, keeping the area clean and dry , using Antifungal powders like clotrimazole
Apart from this zinc based soothing lotions like calamine or creams can provide temporary relief.
Dr smiths cream contains zinc oxide and used for diaper rash but will not be effective for fungal infection.
Since its already been 2 wks , I would advise you to get your child evaluated and treated by his pediatrician
or a dermatologist
for best results.
Wishing you both good health.