I have a 2.5 year old who is spoken only English with me and Spanish with my wife. The one language to one person connection is important so that the child understands the context for switching. (We have a 11 yr girl who went through the same routine and she is bi-lingual although her language development was way faster... she was talking in sentences at age 1) Every child is different. My 2.5 can maybe form 2-3 word sentences...

I personally was brought up with 3 languages (English, Cantonese and Malay), which would be common if you grew up in a multi-cultural country.. no one ever thinks it's a problem there.