I've only just got around to this.... hmm an interesting viewpoint.
I think the tales of sacrifice, particularly the numbers, are very christianised = it would make no sense to sacrifice 1/3 of all healthy children in a tribal society where there were enough risks to reaching adulthood. There are other areas, such as the Auraceipt N'an Eces and Brehon Laws, which make no such indication.
The late Anne Ross would suggest that the Halloween Lantern's would have come from the Celtic head cult. This is well attested (although I'd need to dig her books out of the loft to provide references) and revolved around taking the heads of your enemies with which to communicate with the Otherworld. The story of Bran's head in the Mabinoigen seems to be an echo of this.
It's always good to see another perspective though.
Most dear is fire to the sons of men,
most sweet the sight of the sun;
good is health if one can but keep it,
and to live a life without shame. (Havamal 68)http://gewessiman.blogspot.co.uk