I don't know if this is a common problem but my son from about 2 months had little patches of dry skin on his thighs and another bit started to develop behind his knee when he was around 6 months. These patches gradually got bigger until they were about as big as the palm of his hand. I went to the health visitor about it and she said it could be a slight allergy (maybe down to Johnsons products - she did not think it was eczema), and she suggested bathing him in plain water and moisturising with E45.
This I did for 3 or 4 weeks but it seemed to get a little worse.
As we were going out one day in the hot sun, I put Nivea Sun Children's Lotion - Factor 50+ on him. By the time I got him ready for bed the dry patches had gone (apart from a little discolouration of the skin)- literally in a few hours!!!
I have only used the sun cream a couple of times since, and the dry patches have never returned (the discolouration has also gone now).
I now bath him in bubble bath and moisturise with Simple Baby.
I appreciate this wouldn't work for every baby but it did for DS and wanted to let MNers know in case it could help someone.