I am BAFFLED... all THREE of my kids have eczema!!!?

Ok, It appears it must be something I am doing wrong to cause this because what are the odds of all 3 out of 3 of my kids have ezcema??? Neither me or their dad have it and no one in either of our families have/had it. They dont have serious conditions, but they all have extremely dry prickly skin especially on their legs & knees. They have it all over their bodies except for their faces (thank God) PLEASE tell me what could cause this! Their pediatric Dermatologist has no insight as to why all three have it, and can only say its likely to be hereditary... but like I said...no one else has it. It must be something they are eating right????