K.L.
There can be various reasons for a lack of availability of nutrition in the body. Sometimes, due to hazerdous exposure to lead, mercury, cadmium, alluminum, some vaccines or antiboitics (or even anti-siezure medications), the lining of the intestines can be disturbed or metabolic processes inhibited. Also, if the girls are not identical twins, it is possible that genetic differences could mean a difference in the digestive enzymes their bodies produce. Under any of these circumstances, the body is not always able to assimilate and/or metabolize the nutrients from the foods or supplements they injest. So, just because they swallow it, doesn't mean their body is using it.
Keep in mind that there are many environmental toxins to avoid. Cadmium, for example, is not only present in red and yellow paint, but in second-hand cigarrette smoke as well as fertalizers and weed killers commonly used in lawn and garden care.
I have a nephew who suffered with this. One of the othe factors to consider is that children who eat dirt, feces, etc, are more likely to have parasites that would further compromise nutritional supplies. So, there may be more than one or two types of therapies necessary to see results.
My recommendation would be to seek out a Naturopath or Chiropractor who is a well studied nutritionist. Since so much of what a medical doctor does actually disturbs metabolic balances in the body, they are not as well trained in re-establishing that balance or detoxifying the body from the very toxins they use so commonly. There are times when a medical doctor is the best practitioner for the circumstances. I do feel that you will get better answers with more natural practitioners in this circumstance.
The following info comes from a website I found:
Signs and tests
There is no single test that confirms pica. However, because pica can occur in people who have lower than normal nutrient levels and poor nutrition (malnutrition), the health care provider should test blood levels of iron and zinc.
Hemoglobin can also be checked to test for anemia. Lead levels should always be checked in children who may have eaten paint or objects covered in lead-paint dust. The health care provider should test for infection if the person has been eating contaminated soil or animal waste.
Treatment
Treatment should first address any missing nutrients and other medical problems, such as lead exposure.
Treatment involves behavior and development, environmental, and family education approaches. Other successful treatments include associating the pica behavior with bad consequences or punishment (mild aversion therapy) followed by positive reinforcement for eating the right foods.
Medications may help reduce the abnormal eating behavior, if pica occurs as part of a developmental disorder such as mental retardation.
Expectations (prognosis)
Treatment success varies. In many cases, the disorder lasts several months, then disappears on its own. In some cases, it may continue into the teen years or adulthood, especially when it occurs with developmental disorders.