let me walk y'all through this derivation, because I love this story. this kid was, to my knowledge, the child of English speakers, neither with language deficits. idiopathically, the kid acquired an insanely-small phoneme inventory, described by the SLP as 'practically Hawai'ian.'
one (1) fricative, /h/ (English has eight others).
instead of /k/, this kid has a glottal stop.
no /ɹ/. lots of kids struggle with R, this isn't that weird.
kid says 'I'm,' no problem. kid tries to say 'fast,' but no /f/. kid subs /b/, presumably because voicing a consonant is a lenition rule and so is replacing it with a fricative. no /s/, and a consonant cluster at the end of a syllable is a no-go (also a common problem for younger speakers. we're left with /bæ/.
kid tries to say 'walker,' MOSTLY gets there — but no /k/, so a glottal stop, and no /ɹ/. /wɔ.ʔə/
I'm a fast walker —> "I'm a [bæ wɔ.ʔə]"