What Causes Pimple Like Lesions On Elbows And Knee?

hi my name is melissa. I was just with my son washing up and noticed little pimple like lesions on his elbows and one on his knee. His father and I both have psoriasis but it doesnt look like either of our skin diseases. I am reading that it cld be eczema or a vitamin a deficiency. Should I call the doctor and get it checked out or just try some hydrocortisone cream first?