Anyone with bilingual chlidren?

My son speaks both fluent Russian and English at 3 (we speak mainly Russian in our home, but everyone else around us speaks English) but the doctor is worried my daughter is behind at 17 months, she can say ma ma,da da, hi, that, Jayden (her brothers name), yes, no in English but she also says about 5 Russian words, she understands when we call for her in English and when we call for her in Russian, I believe this is about where my son was at this age too. I have read that bilingual kids sometimes seem behind when they are not.

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    03/14/14
    I don't think bilingualism put our kids behind in their development. My son does an excellent job in our bilingual family ( we speak Russian, Ukrainian and English). Our son didn't speak at all until 2 years old, and I was worry about. This is just his personality, and he is doing just fine in school. We don't have many Russian friends but trying to keep the language for him by speaking Russian and Ukrainian at home.
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    About Anastasiya Belov
    Birth: July 14
    On Moms.com since: Feb 24, 2014
    I am stay at home mother who just recently moved to the US from the Russia. I came here to go school and met my husband. After that we planned a marriage and I moved here in 2009. We have 2 small children and I am a stay at home mom but I do work from home