The motif seems not to have been uncommon in folklore, so I wouldn't read too much into its occurrence in two otherwise-unrelated ballads. The arrow-shooting in Leesome Brand (Child 15) may be more fruitful for you if you are looking for correspondences, but you might want to do some extensive background reading first. Broom turns up so often that it's unsafe to base conclusions upon it; though it often occurs in a sexual context and -sometimes- with a metaphoric function, it's also often just broom!

Child's numbering system is largely thematic, with ballads grouped -to an extent- in related categories; there also seems to be some attempt at a chronological arrangement within those criteria, but you can't rely on it in itself to provide answers. Another problem is that Child died before he was able to write his planned Introduction to the collection, which, among other things, would have explained how his system actually worked.

You have to look at the source information for each text and Child's background notes, too (and as much additional information from other studies as you can) before starting to draw conclusions. Online texts without the notes are, I feel, of little real use to anyone who's serious about the subject.