As far as I know, there are never more than 7 members of the BO worthy of a Spirit nickname. If one of them dies or leaves the organization, they are replaced(Bourbon). So the 7 children might be these 7 members. (there are a couple holes in this theory)
If it's about the seventh child, it would be about a specific BO member. I call Shiho.
But more important, this made me realise how crows are an important theme for the BO. And there is one characters who wears the crows in his name: Renya Karasuma, the owner of the villa in volume 30, which could even be the old nest on the mountain the song refers to.
Ai thinks about a project that has started 50 years ago. The auction in said villa was 50 years ago. Karasuma is said to have died at the age of almost 100. Could it be him the BO are trying to revive? Or is he still alive and kicking, having an entire mafia organization at his disposal? Conan also never solved the mystery of what happened 50years ago. Very uncommon.Also his emblem prominently features a crow.
This is my interpretation of this songs. What are your thoughts about it?

