What is a good product for eczema? ?

If you live near the ocean, regular immersion in sea water is the best cure. Other than that, try using a blend of like 70% kukui nut oil, 30% tea tree oil. Also, it is believed by some dermatologists that eczema is caused by chlorine in the water...so after your 4-year old takes a bath/shower have him/her rinse off with purified water. Like, take a normal shower and then just have like a half gallon or whatever of purified water (warm it up if you want) and then just do a final rinse with that so there wont be any chlorine residue left on the skin. Also, consider using shampoo as a body wash instead of soap because shampoo is milder and less drying.

Have you tried bleach baths?  This is standard treatment in the UK.

You can use tea tree oil applied to the areas as well as coconut oil at nights. Also honey applied to the areas helps. Use very gentle soaps to bath with