I am a native english speaker settled in the Netherlands; I speak fluent (but not very grammatical) Dutch. I now have a granddaughter Rosie of two months and her mother (my step-daughter) has suggested that I speak only English to her, so that she will grow up bilingual (a variant on the One Parent One Language (OPOL) approach). They live close by and we see them almost daily.
This sounds like a good idea to me, but which language should I use with third parties (typically the mother and the grandmother, my wife) in Rosie's presence? Should I answer their Dutch questions in Dutch or English? All parties involved (family and friends) speak enough English to handle both languages. My automatic reaction would be Dutch, but I think I can train myself to always use English in Rosie's presence.
Conversely, how important is it that the Dutch people speak Dutch? For example, I recently said to Rosie: "That was a nice big burp" and my wife echoed me with "Another big burp then" instead of the Dutch equivalent "Nog een grote boer dan" which she would have otherwise said. Will Rosie get confused in such situations?
Fortunately we have a few months before Rosie will actually begin to recognise words, but I'd appreciate advice, both for me and the other parties.
Extra information if it's relevant: the father is absent but visits occasionally, is Dutch-speaking. Rosie will have very little other exposure to English apart from TV and adverts (English is very trendy in Dutch adverts). Rosie's biological grandfather died in a car accident, I married his widow and have excellent relations with the children (Rosie's mother and uncle).