Well I did query it with them and have had this reply:
Hello Surfermum
I can understand your confusion about why childrens' nappies would be
removed under our Adult Materials policy. Your items were ended for the
specific reason of being used nappies. Now, while I believe that you are
not selling these items as though they are a type of fetish material, we
do have members on our site who try to sell their used undergarments in
such a fashion. As such, we have decided to put our Used Undergarments
policy under the Adult Material policy.
Although I know you only had the best intentions when selling these
items, eBay does not allow the sale of used nappies for children to be
sold on the site under any circumstances. You are free, of course, to
list brand new nappies on the site.
eBay does not permit the sale of any used undergarments. Used
undergarments would include, but are not limited to: athletic
supporters, boxer or jockey shorts, bras, briefs, full-length panty
hose, panties, and thongs.
Any hint or insinuation in the auction listing that the undergarments
have been previously worn will not be permitted.
The body drizzle does not violate any of our policies and would be fine
to list.
Thank you for your patience and understanding.