Cantilever brakes for BMX?

Hi All,

My 7yo son has a BMX but is unable to pull the brake levers on
hard enough to stop without hitting something (usually me).

Is there a way of mounting cantilevers with a bit more leverage
onto a frame without the bosses? (and without braising some on).

Maybe like a U frame with the bosses mounted on it that clamps to
the original brake pivot and maybe the seat stays or forks?

Or, what about dual pivot brakes - I have them on my roadie
can you get them for BMX tyre/rim?
(note that the rim is Al, so it should stop OK?)

thanks,
Matthew

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