To do a thorough search for scores in UM Libraries, do not limit your search to the Performing Arts Library.
At College Park, a substantial number of scores are in microfilm collections at McKeldin Library.
Some scores not owned in College Park Libraries are in the USMAI Libraries system. In the catalog, searching USMAI (all campuses) broadens your chances of finding what you need.
For example, doing an all-campus search on 'children's' as subject word and 'scores' as format will yield 407 hits. Doing the same search with just UMCP as location yields only 373 hits and searching just in the PA Library yields only 254 hits.
A note on Juvenile scores
Scores deposited as UM theses and dissertations are available for study in the PA Library, the Maryland Room at Hornbake Library, and, full text from 1997 to the present, in Digital Dissertations Full Text, where dissertation scores from other universities are also available to UM Libraries researchers.