I am a linguist and have four children. My wife and I also have different mother-tongues - English and Spanish. Because one of my children had speech problems, I have done a bit of research into this topic. The bottom line is that kids have an amazing ability to pick up on language. If they grow up hearing two or three languages, in different contexts, they will learn them and distinguish them, easily.<p> I would encourage you to speak whatever is comfortable for you to use in each context. Don't try to force one of your languages into a situation so that your child will learn it, because you will not be consistent and that might add unnecessary confusion. But as long as you can be consistent, in a particular context, with your language use, I would not be worried about your child being able to keep things straight. The brain's ability to learn and process multiple languages, at that age, is astounding.<p> However, as with all things in raising a child, be watchful, observant. If your kid struggles at some point, you may have to adjust. When one of our kids' speech regressed from age 2.5 to 4, we were of course very worried. After seeing a speech pathologist, a psychiatrist, and a neurologist, we found that he was severely impaired in speech comprehension and production. He was diagnosed with a rather severe form of Autism. Because of this, we limited our language at home to only English, my wife's native language, and started an intensive regime of speech therapy at home, designed by my wife. Now, 13 years later, he is highly successful in school, taking AP classes in high-school, and being recruited by top schools like MIT, Caltech and Harvard.<p> Ok, could not resist the little bit of bragging on my boy. But the point remains - do what is comfortable language wise. Do not try to use a language just so the child can learn it, but don't rule a language out because you think she may be confused by too many languages. Speak whatever language comes most naturally to you in each context, and be consistent, but be watchful and be ready to adjust to each of your children's individual needs.