You can treat soap vaginitis with baking soda and warm water soaks. Dissolve 4 tablespoons of baking soda in a bathtub full of warm water. The baking soda will help get any stubborn soap, urine or other irritants off of your little one’s genitals, which will speed up the healing process. Let your child soak in the tub for 10 minutes twice a day for two days — and follow up with a humectant to seal in the moisture and prevent itching.