From the symptoms and pictures,it looks like nummular eczema(stubborn, itchy rash that forms coin-shaped patches on the skin.Found mainly in adults but can oocur in children also) , hives(red, itchy, raised areas of skin that appear in varying shapes and sizes. They have a tendency to change size rapidly and to move around, disappearing in one place and reappearing in other places, often in a matter of hours.Many cases of hives are "idiopathic," meaning no cause is known. Others may be triggered by viral infections or medications), or granuloma annulare(bumps appear over the joints and the backs of the limbs).
I feel that you should discuss these three possibilities with a child pediatrician as treatment for all is different.You can log on to the following website to visualise the rashes in all these three conditions: http://www.visualdxhealth.com/searchResults/child_Female_Leg.htm
Hope it helps.Take care and pls do keep me posted on how your child is doing and if you have any additional queries.
Food allergies...my niece had chronic idiopathic eczema for years. It used to bleed it was so bad. 2 weeks gluten free and it mysteriously cleared up. The pediatric dermatologist thought it was all the creams she was prescribed that must have finally worked after 3 years on them. We knew better. So many skin reactions are the body's response to food intolerances.