Hi! Emma:
I am quite disappointed too in that H2, H3, etc are not included in the TOC, only H1 is. But this applies to the HTML format of pages.
As I just found out, some of my students used the Nwiki format, and there the TOC and associated coding/tags worked (at least at two levels). Personnaly, I had recommended the use of HTML pages to students, but I may reconsider once I take a better/closer look of the Nwiki format.