By own family experience I can attest to the fact that raising bilingual children is difficult and time consuming. I recommend creating a firm foundation not just in receptive but also in productive skills. In other words, teach writing and speaking and give authentic purposes to children to use it. It worked for us. Our child, in 8th grade, just passed a college language placement exam in our home language after 20 minutes on graduate student level. So, keep it up and don’t let anyone tell you that it cannot be done.
A proud mother
Read this Blogpost from another about her experience: http://www.multilingualliving.com/2013/02/04/raising-bilingual-children-the-non-native-gone-astray/