In bilingual child language acquisition research, a recurrent learnability issue has been to investigate whether and how cross-linguistic influence would interact with the non-adult patterns of omission/production of functional categories. In this paper, we analyze the omission/production of subject pronouns in the earliest stage English grammar and the earliest stage Spanish grammar of two English–Spanish simultaneous bilingual children (FerFuLice corpus in CHILDES). We base this analysis on Holmberg’s (2005, Is there a little pro? Evidence from Finnish. Linguistic Inquiry 36. 533–564) and Sheehan’s (2006, The EPP and null subjects in Romance . Newcastle: Newcastle University PhD dissertation) formulation of the null subject parameter and on Liceras et al.’s (2012, Overt subjects and copula omission in the Spanish and the English grammar of English-Spanish bilinguals: On the locus and directionality of interlinguistic influence. First Language 32(1–2). 88–115) assumptions concerning the role of lexical specialization in cross-linguistic influence. We have conducted a comparative analysis of the patterns of production/omission of English and Spanish overt and null subjects in two bilingual children, on the one hand, versus the patterns of production/omission of one monolingual English child and one monolingual Spanish child, on the other. The results show that while there is no conclusive evidence as to whether or not English influences the higher production of overt subjects in child bilingual Spanish, the presence of null subjects in Spanish has a positive influence in the eradication of non-adult null subjects in bilingual English. We argue that in a bilingual situation, as compared to a monolingual one, lexical specialization in one of the languages of the bilinguals (the availability of an overt and a null realization of the subject in Spanish) facilitates the acquisition of the other language.