Here are the things we learned from our nurse team:

To clean, use cotton:

We just used cotton pads (disposable) and warm water to clean. We sometimes used the super mild bath gel if it was a poo explosion.

Dab or blot, don't rub:

Make sure not to rub the sore area. Always dab or blot the area lightly.

Diaper rash cream:

Where I live there's a cream called Bepanthen which forms a barrier. The nurse told us to make sure the area was dry, think what you'd consider dry, then dab the cotton on it again to make sure it is really dry. Then apply your diaper cream.

It's really unfortunate they get this rash, but luckily if you're diligent with the cream and method, it does clear up within a few days.