Early childhood language experiences influence how a child's mind and brain process language and acquire literacy. For children growing up bilingual, their two languages interact in their minds, and these cross-linguistic influences can lead to unique neurocognitive mechanisms for language and reading compared to monolinguals. In this dissertation, I asked: "how does early bilingualism impact children's cognitive and neural organization for learning to read?" To address this question, this dissertation includes three inter-related studies of behavioral and functional Near-Infrared Spectroscopy (fNIRS) neuroimaging assessments with young Chinese-English bilingual, Spanish-English bilingual, and English monolingual children (N = 283, ages 5-11). Children completed language and literacy tasks in each of their respective languages while their parents completed questionnaires on children's language use. Studies 1 and 2 revealed that bilingual children processed English words in a way that reflected their proficiency with the characteristics of their heritage language -- in particular, Chinese bilinguals relied more on meaning-based skills, whereas Spanish bilinguals on sound-based skills, to read English words (Study 1); and in both groups, higher heritage language proficiency is associated with stronger activations in the left temporal brain region when processing English words (Study 2). Study 3 further revealed that bilinguals with stronger dual language proficiency formed more widespread neural connections within the neural network for language processing. Taken together, the findings suggest that heritage language influences children's literacy development and emerging neural organization for learning to read and these bilingual influences reflect children's experiences and proficiency with both of their languages. These findings thus inform theories of bilingualism and literacy instruction for children from diverse socio-linguistic backgrounds. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]