Well, it certainly seems like "London" is more interested in the confinement side of things now doesn't it? Yes indeed. First and foremost, this is a poem about literal forms of confinement: chartering, a way of controlling, narrowing, and confining things that should be open (like rivers and streets). Then we've got that chimney sweeper, who for all intents and purposes is a slave worker; ditto that soldier (he's gotta do whatever the government tells him). On top of all this, there's those pesky "mind-forg'd manacles," the poem's metaphor for all the ways in which people dream up (that's the mind part) to enslave people. This could be governments planning wars, or governments mismanaging geographical space (the Thames, the streets), or even random people looking at things all wrong.
Free?! There is nothing free about London. Even children, the most "free" of all, are slaves—to the church (as chimney sweepers), to fear, or even to the corrupting curse of the harlots.
Not even the speaker is free in this poem. Just look at how the language of this poem is confined—the repetition of sounds and words mimics the poem's themes.