I just got a new advice from a colleague at the office (she got this from her own children’s speech therapist):
Don’t speak to your children with language that is NOT you mother language!
Because your children will imitate you and especially your accent and ALL of your grammar mistakes. So, if you ever consider to raise bi-lingual (or multi-lingual) children, consider YOUR OWN linguistics skills. It’s actually better to let them learn foreign language by a teacher or other people with better accent and grammar. Thus, just speak to your children using your own language, the one that you know best about all the grammars and intonations. Don’t worry about your children linguistics ability, because a child’s brain will develop in time and without you’re realized, your children are already speaking in multiple languages! Even far more better than their parents!
Oh, by the way, the colleague of mine are from Argentina and she fluently speaks Spanish (naturally!) and because of this advice, she only speaks Spanish to her children. Now her children, ages 4 and 2, are speaking Dutch, English, and Spanish. Her children are quickly switching into Spanish whenever they want to talk to her.