We investigate whether dominance, language experience, and increased interaction have an effect on the development of heritage bilingual children’s knowledge of the discourse-pragmatic constraints guiding null and overt subjects. A group of child heritage bilinguals (n = 18, mean age = 5;5) and comparison groups of adults: Mexican Spanish monolinguals (n = 15), heritage bilinguals in the United States (n = 16), and English monolinguals in the United States (n = 16) completed a language background questionnaire, a portion of the Bilingual English-Spanish Assessment (BESA) in English and Spanish, a forced-choice task (FCT) in Spanish, and two acceptability judgment tasks (AJT s): one in English and one in Spanish. Results showed that heritage children and adults pattern similarly and differently from adult monolinguals. Increased interaction at home has a positive effect on accuracy in the pragmatic conditions that license null subjects in Spanish without affecting overt subject patterns in English, the dominant language.