To clarify:

No, I don't think it's appropriate to take nude photographs children;
No, I don't think children are capable of giving informed consent;
Yes, I do think their parents were, frankly, stupid (possibly starstruck) to consent to the photographs;
No, I don't think the "but it's art" argument excuses everything under the sun;
No, I don't think Mr Henson should have taken those portraits; but
No, I don't think Mr Henson is a pornographer.
That some sad, sick people may get off on those photographs is unfortunate, but that does not make it porn. That argument would make Anne Geddes the greatest child pornographer ever. Her work may be sickly sweet, cloying, saccharine, and some of her photos of older children are a little disturbing (go look at her galleries), but it's not porn.
Still, I'm sure there are sad and sick folk out there that trawl her website, buy her cards and posters and get off on her pictures of naked babies and young children. Perhaps if the parents of her models thought of that they wouldn't have consented to the photographs being taken.
Look, there are some people who get off on feet, that is their thing, but does that make this porn?

No. And that is all I'll say on the matter.