Both my 6 and 3 year-old are fully bilingual. My 6-year-old can even translate between languages easier than I can! We are a mostly One Person, One Language (OPOL) household. My husband only speaks English and I only speak French to the boys. Although I speak English to my husband at home and also to other people outside of the house (which is not OPOL) they know to speak to me in French. I started speaking French to them from birth and it felt very natural to me as it is my mother's tongue. However I believe you do not have to be a native speaker to introduce your child to a new language.
Around 2-year-old my boys started speaking a mix of French and English, sometimes mixing whole words or just sounds within words (carture: car + voiture). Around 3-4-year-old they started making the difference and associating a person with a language. That being said, whoever is the minority language (in this case I am) will have to work harder to get the language through.
At home we have implemented a few strategies to help them with the separation of languages and the French learning:
Community: I always search for a French community where we live. In Las Vegas the community was rather large so it was easy, however where we live now has been more of a challenge as it is a smaller town. We have found a small community that has events and we are making friends with some of the French parents. Although the kids tend to speak English together they still get the benefits of a hearing a lot of French and seeing a lot of French culture.
I found my first community on Meetup.com and the community here on Facebook.
Traditions: even though it's often just the 5 of us I follow the French traditions and we celebrate the French holidays. I also have a lot of books to go along with them so I can explain to them what it is all about.
Activities and learning at home: we do a lot of learning and art activities at home and one of the main purpose is to introduce specific vocabulary they would not know otherwise.
That being said there are many more ways to introduce several languages to your children, and it can even be 3 or 4 languages if you know them! Some of the other strategies are:
▪︎ minority language at home
▪︎ time and place (each place or different days of the week get a different language)
▪︎ I'm also a big believer that any exposure is beneficial even if there is no method or if you are learning the language together!