I feel as though the source is music tag should not have children that are songs that are typically sampled. For example, currently Hammer is a child of the source is music. This doesn't really make sense with the way the site is set up. Yes, in most cases it will be used as a source, but as the case with any song it is just as possible for it to be used as a BGM. In that case (rare as it may be) it should not have the source is music tag, but if it is a child it would still come up in search.

Ideally, parenting should only be done in cases where the child is fully encompassed by the parent's parameters, so in this case, only when you can be absolutely sure that the song will never be used as a BGM. Obviously, you can't be sure of that in any circumstance, so this kind of parenting should not be done.