Green’s Dictionary of Slang

babbling (brook) adj.

[rhy. sl. = crook adj. (2)]

(Aus. / N.Z.) unwell.

[Aus]Sun. Times (Perth) 25 Apr. 35/2: Babbling brook for crook.
[NZ] McGill Reed Dict. of N.Z. Sl. 14: babbling brook [...] Unwell, as in ‘crook’.