My daughter has eczema, but it wasnt really a problem except for a few dry patches until she was 5. She is now 9. Each winter since she was 5 her hands get so dry and itchy and they start to crack and bleed. The first winter we were getting a prescription lotion of some sort, I dont remember what, but there was a warning on it to not ingest it. Now everyone knows 5 year olds arent that careful with their hands. I saw her spill yogurt on her hand and lick it off.So I went back to the doctor and told him I didnt want her having that stuff on her hands anymore, even though it worked wonders. He suggested the baby lotion that contains collidal oatmeal in it, and the collidal oatmeal baths on a regular basis. (I can't give you the brand name here I dont think.) Most stores carry it in the baby section by the diapers and wipes and baby soaps. It works for us. There are some other things you can do to help too. In my child's case, I found that its the cold harsh weather that brings it on mostly. Therefore before she goes outside for longer than just to get in the car, I lotion her up, every single part of her body. I then make sure she is double layered to keep the cold dry air off her skin. Usually long johns, top and bottom, under her outfit. She has to wear gloves, one trip outside will suck the moisture right out of her hands and we then have a problem because its too late and have to constantly apply the lotion until it clears up.
You have to find out what triggers the eczema or psoriasis in your child, every one is different. Experiment with different things to clear it up. Then you can be prepared.