Is repivate safe to use on a 6week old's skin?

Maybe: This is a steroid cream that is occasionally used with inflamed skin. Chronic use can lead ti thinning of the skin & subsequent problems. You did not mention the strength, which matters. I rarely use more than 1/2% & not more than 2X/d, never near the face. Kids at 6 whs rarely need this as their neonatal acne will clear with age. It just needs to be kept clean.