Well I don't have kids but my levels have changed. Before I was eating normally, and several years later, now, I should only be eating 10 grams of protein.
When i ate normally my levels were in the teens and I was in middle school and high school at the time. Between then and now (20 years) I have become less tolerant of protein. My levels get as high as 1965 micro-moles per liter which is around 33 mg/dl. At 10-15 grams my levels are ~800 which was where my levels were when I was much younger.
So yes the do change and I don't know how many doctors believe this but it happens.