I just did a quick survey of the literature as well, and it appears that the areas that are usually most impacted in children are working memory/executive functions, processing speed, and perceptual reasoning. Also increased anxiety and mood disorders. Granted, all of the research consists of small-scale studies, from what I can see.
Adult research suggests that the deficit is a higher-level one, of integration and organization.
I would also encourage you and your DC to look into some of the Lyme Disease forums, support groups, etc.
Also, regardless of the long-term prognosis (I am not suggesting one way or the other), there is a kind of grieving process that individuals and families go through when the temporary or permanent loss of a prior level of cognitive function occurs. For resources on managing those kinds of feelings, I would suggest looking up TBI (traumatic brain injury) groups:
http://www.biausa.org/brain-injury-community.htm
