The Times of 30 June, quoting the Reading Mercury, has the following: “A Monster.—A day or two since, a gentleman travelling along the road near Colnbrook, had his attention attracted to the screams of a child in the care of a tramping woman, who had with her, two other children totally blind. The cries of the child were so distressing, that he insisted on knowing the cause; but; not getting a satisfactory answer, he forcibly removed a bandage from its eyes, when, horrid to relate, he found these encased with two small perforated shells, in which were two live black beetles, for the purpose of destroying the sight. The woman was instantly seized, and given into custody; and, at the magistrate’s meeting, at Eton, on Wednesday last, committed for trial. There is too much reason to fear that the wretch produced the blindness of the other two children, by similar means.” This was rendered into a street ballad.
Is it true? I don't know; but it was reported in the press (Friday, Jun 30, 1843 in the Times). The book in which I discovered this gem is Gossip in the First Decade of Victoria's Reign and, although little more than a collection of news clippings compiled in 1903, not a bad read in itself.
See this link ...
(many thanks to the commenter below)
But is it a genuine case or a fantasy? ... still digging ... my guess is still urban myth, as I can't find a fuller account anywhere in the British Library newspaper databases; combined with the unknown place name in the ballad ... but I could yet be proved wrong.