Learning two languages is an easy thing to do -- if you are a baby! When a baby is immersed in a loving family where two languages are spoken, the baby has little trouble absorbing the sounds of both languages and keeping them separate in her mind. This is especially true when one parent speaks to the child in one language while the other parent speaks to her in the second language.
This is how my granddaughters are being brought up, speaking English and French, and to watch the way they absorb the sounds and communicate in both languages amazes me! This isn't to say everything is perfect and they never make a mistake. They have their adorable mix-ups as any baby learning even one language will have. However, for every item in their world, they have two vocabulary words -- one English and one French.
My son Aaron was born in Canada and grew up in both Quebec and Vermont. He learned French while still young and speaks with hardly an accent. He met his wife, Marianne, at College.
When their first baby was born, Aaron and Marianne decided that Aaron would speak only English to the baby while Marianne would speak only French. That way there'd be a "Mommy language" and a "Daddy language."
Because both parents are bilingual and their daughters know it, there have been some challenges keeping to the two languages rule, but in general, it is working out quite well. As a family, they can now flip back from one language to another without a problem. The girls are very aware, however, that their grandparents are not quite so lucky! They must feel they are much smarter than the older folks!