This paper is concerned with a specific case of L3 acquisition: the starting position for English vowel acquisition by infant German-Italian bilinguals will be investigated in light of prototype theory. The chosen example of triple language contact is characterised by consecutive bilingualism as the basis of L3 acquisition, where the learners' L2 is typologically related to L3. It will be discussed whether extended competence in a Germanic language may constitute the basis for transfer in phonetic acquisition of a further Germanic language. The investigation is embedded into a threefold framework: (1) considering the linguistic plurality of the European Union and its educational and linguistic policy, it examines the status of English as L3 in Europe; (2) according to the learners' psycholinguistic characteristics, it discusses the age issue in L3 phonetic acquisition; and (3) against the background of contrastive analysis, it illustrates differences and similarities between German, Italian and English phonetics, and phonology. Within this framework, infant bilinguals' German and Italian vowels will be phonetically analysed and compared with English target vowels. The implications for L3 phonetic acquisition based on the findings are intended as a preliminary, small-scale investigation in preparation of a wider study on a longitudinal basis. The findings presented here are of interest wherever learners share the characteristics of the study participants: bilinguals that add an L3 to their bilingual competence before completion of the so-called critical period. (Contains 4 figures.)