Some Brief Conclusions...
The differences between William of Newburgh’s account of the green children and Ralph of Coggeshall’s account is probably due to the differences in how each author originally heard the story. William appears to have investigated the story around forty years after it happened and talked to many people who recounted the event to him, so his version is likely a smoothed-out compilation of many short versions of the story. Certainly, he did not state that he talked to any eyewitnesses; so it’s quite possible that none of the people he talked to were.
Meanwhile, Ralph appears to have heard the story repeatedly from just one man who claimed to be not only an eyewitness, but a vitally involved character. This sounds suspiciously like said ‘eyewitness’ -- Richard de Calne -- may have been bragging to Ralph, and should make us suspicious of his claim of direct involvement in a locally famous tale. The simple fact that de Calne’s name is not mentioned in William’s account, despite the fact William interviewed numerous people, may be a strong indication that de Calne was not originally involved in either the event or the legend.
Although both accounts agree on the general structure of the story, they disagree on the details; so they cannot be used either to confirm one another, or to prove the event happened. Still, each has clues that narrow down the where and when of the event, so further digging may still be able to give a more definitive answer in the future. Of course, it would help if there were a third ancient account, but...
Gervase of Tilbury's Account?
I have run across a small number of authors who have claimed that a third ancient account of the green children exists, written by Gervase of Tilbury, a well-known author of historical texts. Since Gervase lived from around 1152 to 1220 CE, an account from him would be as valuable as Ralph of Coggeshall’s or William of Newburgh’s; unfortunately, I haven’t found any real indication that Gervase actually wrote such an account.
The claim that Gervase gave an account of the Green Children of Woolpit was first put forward by Harold T. Wilkins in his book Strange Mysteries of Time and Space, published in 1958, and it is from his book that all other authors repeat this claim. But the quotes that are presented by Wilkins’ in his book from the so-called Gervase account not only add nothing new to the story, they are also clearly a simple blending of the details previously recounted in both Ralph of Coggeshall’s and William of Newburgh’s accounts. For example, Wilkins’ gives a quotation from the green girl that he claims is from Gervase’s account, but it is nothing more than an unskillful paraphrasing of Stevenson’s translation of William’s same quote from the green girl5.
There are other suspicious similarities between Wilkins’ “Gervase account” and those of Ralph and William. Wilkins says that Gervase’s account states that the girl married at man at Lynn, and Wilkins then quotes, “where she was said to be living, a few years since.” When compared to William of Newburgh’s account: “...she was married at Lynne, and was living a few years since, at least, so they say...”, it becomes clear that Wilkins is giving a simple paraphrase of William’s line as a supposed quote from Gervase. Wilkins’ alledged account from Gervase of Tilbury offers only one detail different from both Ralph’s and William’s accounts of the green children; it claims the beans were given to the children while they were still sitting in one of the wolf-pits.
So Harold Wilkins is the only actual source I’ve found for a claim that Gervase of Tilbury wrote anything about the green children, and the evidence leans heavily towards the conclusion that Wilkins created the alleged account himself. Though he implies that the story may have come from Gervase’s famous historic text, the ‘Otia Imperialia’, Wilkins never clearly states this as a fact; and I have found no other indication that the green children story is in said text. For this reason, and the others already mentioned, I will need to see more evidence before I’ll believe that a third ancient source for the story exists.