Language exposure plays a large role in language acquisition, and bilingual children must acquire both of their languages in environments that typically include abundant speech variability. The specific goals of this dissertation were to examine how speech exposure affected phonological retuning and lexical access in bilingual children's second language. In three experiments with Spanish-English bilingual school-aged children, three types of speech typical of a bilingual environment were compared: native English, native Spanish, and Spanish-accented English. The experiments tested the relationship between speech exposure and changes to the bilingual production and perception systems. Experiment 1 focused on phonological retuning in perception, and examined whether categorization of voiced and voiceless stops would be affected by exposure. Results showed that bilingual children were more likely to relax categorization criteria after exposure to native Spanish speech and were more likely to shift category boundaries to more English-like levels after exposure to accented speech. Experiment 2 examined phonetic imitation in production which entailed children producing stop-initial words. Perceptual and acoustic judgements of words indicated that only children with higher phonological memory were likely to converge to presented speech, while those with lower phonological memory sometimes diverged. Lexical access was examined in Experiment 3. Bilingual children did not differ in accuracy of picture recognition in English after the three types of exposure, but only after native English exposure were English words strongly co-activated. Spanish words were co-activated after both native English and native Spanish exposure. After accented speech exposure, English word were minimally activated, and Spanish words were not activated Findings suggest that exposure to L1 speech does not strongly affect L2 production and perception in bilingual children, and exposure to accented speech, especially for those with lower L2 language abilities, sometimes leads to perception and productions more similar to a native speaker of the L2. This makes accented speech a potential tool for developing more native-like perception and production abilities. The results can also assure bilingual caregivers and speech language pathologists that although variety in language input slightly affects the language system of bilingual children, the changes are not large enough to affect overall comprehension. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]