I have never seen swelling at the back of the neck described as a CH symptom. Not saying it isn't . . .
You might consider emailing Batch, the fellow who developed the D3 regimen and who follows it very closely. He is a great guy -- a true CH hero, in my book -- and it's almost certain that he will respond to any questions you ask him. He might not know anything about D in kids, but it's worth asking him, I think. Email him from here: https://clusterbusters.org/forums/user/17422-batch/