Introduction

Published research on children's speech development is mainly related to studies of monolingual English-speaking children (Zhu & Dodd, 2006). More recently, there has been increased interest in children acquiring other languages (e.g. Ballard & Farao, 2008 for Samoan; Fox, 2000 for German; MacLeod et al., 2011 for Québécois French; To et al., 2012 for Hong Kong Cantonese). Research suggests that children acquiring different languages have some language-specific developmental phonological processes indicating that findings for one language are not applicable to other languages (e.g. Amayreh & Dyson, 1998 for Arabic; Grech, 1998 for Maltese; Macleod et al., 2011 for Québécois French; So & Dodd, 1994 for Cantonese; Zhu & Dodd, 2000 for Putonghua). During the past couple of decades research on bilingual acquisition has become of more interest.

Studies on bilingual phonological acquisition include those for Spanish-English (Fabiano & Goldstein, 2005), Cantonese-English (Holm & Dodd, 2006), German (Lleó et al., 2003), Welsh-English (Munro et al., 2005), Arabic-Swedish (Salameh et al., 2003) and French-English (Sundara et al., 2006). There are indications that children exposed to early sequential bilingualism show different patterns of phonological acquisition from those of monolingual children of the respective languages (e.g. Grech & Dodd, 2008; Holm & Dodd, 1999c). Further, sequential bilingual children may exhibit differences in type and number of errors from simultaneous bilingual ones (De Houwer, 2009). When Wright and Gildersleeve-Neumann (2005) compared 11 monolingual English-speaking children with five Russian-English bilingual children (two of whom learned Russian and English simultaneously and three of whom acquired English once their Russian was established), they found that the sequentially bilingual participants made more consonant errors than the simultaneous bilingual children and that overall the bilingual participants made more errors than the monolingual subjects.

The finding that bilingual children's phonological acquisition differs from that of monolinguals of either of the languages spoken indicates that having two phonologies affects the course of acquisition. This is in line with the Interactional Dual Systems Model for the mental organization of more than one language.