Do bilingual children learn two languages faster than monolingual children learn one language? Do children from bilingual families learn two languages faster than children from monolingual families learn one language? In other words, I'm wondering if there's a language learning advantage to growing up in a bilingual home. If that is the case, what about for families that speak 3 languages or more?
I think it's all about passion for languages. I have bilingual children and my first was having difficulties with my native language compared to the second one. It's all individual...So the answer is 


  it depends


in my opinion I think there is no advantage over the children from monolingual. Children from bilingual families take 2 different languages as one. So in some sense there are still monolingual... 

here is some paper:


  Because a key expectation parents have is for their child to perform
  well in school, it is important for parents to know that bilingual
  children and monolingual children develop their learning abilities at
  different speeds. Children learning two languages learn each language
  more slowly than monolingual children learn their native languages. It
  is easy to understand why -- children have a limited amount of time
  with which to dedicate to listening and reading language; if a child
  is bilingual, he will split that time between the two languages, which
  slows his learning speed. This often affects the academic performance
  and communication skills of bilingual children, which can cause stress
  in the family. In a sense, the average school is set up to go at a
  monolingual speed, which might outpace bilingual children.


http://everydaylife.globalpost.com/child-development-bilingual-vs-monolingual-household-7371.html


  Bilingual 12-year-olds perform worse at school than their monolingual
  peers, a researcher at Sweden's Örebro University has found.


http://www.thelocal.se/20110323/32766