This is my first official post, so apologies if I get things wrong, either etiquette-wise or technologically…
It would be interesting to see what assorted ‘illiterate’ subjects to with other allophones of /t/. David Stampe told me years ago of children who systematically replaced their parents’ glottal stops with slightly aspirated [t]’s in word such as ‘kitten’, ‘mitten’. This was particularly interesting since the adults never said [mIt@n].
Given his views, of course, what the children were doing was perceiving the intention and pronouncing that, since they didn’t yet control glottal stops. That doesn’t explain why children would systematically revert to the voiceless underlying target in non-alternating contexts however.