This study contributes to the analyses of transfer in the case of typologically similar and typologically different language interactions from three different perspectives: L1, modality and time of instruction. To do so the L2 English sentential subjects produced by 26 L1 Spanish, 26 L1 Bosnian and 26 L1 Danish children are analyzed. These L2 English participants are divided into two proficiency groups depending on the time of instruction received (2 or 4 years). Written production data (story-telling) were obtained by means of a wordless picture sequence adapted from the Edmond Narrative Norms Instrument (Schneider et al. 2005) which participants had to narrate. Oral production data were obtained through a semi-guided individual interview which was audio recorded and then transcribed in CHAT (Codes for the Human Analysis of Transcripts) format (CHILDES, MacWhinney 2000). The subjects produced by these participants were classified following three criteria: form (overt vs. null), grammaticality (grammatical vs. ungrammatical) and adequacy (adequate vs. nonadequate). Two formal proposals on sentential subjects are tested against these L2 English data: Holmberg (2005) and Sheehan's (2006) with regards to [+null subject] languages being superset to [-null subject] languages; and Fernández Fuertes & Liceras (2018) and Liceras & Fernández Fuertes' (2019) on the so-called lexical specialization approach that accounts for both directionality and effect of cross-linguistic influence. The results show that typological similarity is a conditioning factor in what regards both core grammatical structures and syntax-pragmatics interface related issues. Time of instruction, however, does not have any effects on these children's L2 English acquisition of sentential subjects. In the case of modality, the written task is proven to be cognitively more demanding. These results offer a new window into the analysis of English L2 subjects in that they not only confirm the vulnerability of interfaces also in the case of under-studied languages, but they also show how Liceras & Fernández Fuertes' proposal applies to L2 acquisition: cross-linguistic influence from the superset language (i.e. Spanish and Bosnian) results in positive transfer. This investigation is part of the research funded by the Castile and León Regional Government and the ERD (European Regional Development Fund) under Grant Ref. vi VA009P17, and by the Spanish Ministry of Science, Innovation and Universities and ERDF under Grant Ref. PGC2018-097693-B-I00. I am also very grateful to the Department of Investigation, Innovation and Transfer and the English Department at the University of Valladolid for making this financially possible. A space was also provided to me at the University of Granada. I am very grateful to Cristobal Lozano and his ANACOR team for letting me join in. I have, at all times, been treated as any another member. A special thanks goes to Teresa Quesada and Fernando Martin Villena for taking their time to discuss both academic and personal issues and ...