Brian,
If no-one else is offering I can easily check the Journals for the first mentions of Child. In fact I'd enjoy that. I can not possibly conceive of anyone in this country connected with folksong from 1888 onwards not being familiar with the Child Ballads. Baring Gould certainly was as he was sending material to Child and asking for copies as they appeared, in return for his contributions. What I do find strange is they seem not to have been given any extra status over the broadside ballads until Sharp went to America.