E.O.
With my daughter I clean her off, at bedtime, in detail (down there) with wipes then put 'Monistate cream' on her. I have to do that for a few days, and she'll be fine for a while. I usually have to do this once every two months. My daughter's now 6 1/2 and I've been doing this since she was three. Good luck!
Also, laundry detergent is key for me and my kids. We all have very sensative skin. We use 'Tide' or 'Dreft' detergent, 'Kirtlnd' brand or 'Downy' fabric softener, and 'Bounce' dryer sheets. Any other brand causes irritation of some kind on one or more of us.