You can grab these pretty much as soon as you get to London, and the low level enemies shouldn't case you any problems.
Secret #22 - Whitechapel
The music box is along the train tracks to the northeast of the Whitechapel viewpoint.
Follow the tracks in this area until you spot a wooden hut off to the side.
The music box is on the ground just in front of it.
Secret #26 - Whitechapel
You can find the music box in the cemetery of St. Mary Matfelon church.
The church is to the southwest of the Whitechapel viewpoint.
Head around to the right and past the statue.
You'll find the graveyard back here.
The music box is on top of the grave next to the tree.
Secret #18 - Whitechapel
This Secret is to the southwest of the Whitechapel viewpoint.
With the viewpoint behind you, walk along the street until you spot the building with graffiti on the wall next to the benches where the urchins are hanging out.
Climb up and head to the roof of the next building.
The music box is up here.
Secret #29 - Whitechapel
The last of Whitechapel's Secrets is to the southeast of the viewpoint.
Head east from the viewpoint.
There's a path that leads off the street to the right.
Head straight down here, sticking to the right side.
Pop through the doorway and gate at the end, and into the small park beyond.
Go past the tree and head left at the statue.
The music box is on the floor of the alley.