Input-driven differences in toddlers’ perception of a disappearing phonological contrast

How does phonological development differ in children exposed to one versus two variants of a single language? If children receive mixed evidence for a phonological contrast (i.e., one language variant in the environment maintains a contrast while another neutralizes it), will they treat this contrast as noncontrastive (i.e., as allophonic)? Or will they learn that only some speakers maintain the contrast and use this information to strategically...