I've always been of the opinion that I would eventually have children. I've also always believed, since age 25 or so, that raising children to be bilingual would be beneficial, pretty much regardless of the languages involved.

Learning earlier is easier, and will be helpful for the future.

Happily I married a Finnish woman, and we've agreed we'll use both languages all the time. (Helpfully I'm also learning Finnish at the moment).

The (local) people I've seen do things seem to either repeat words in both languages, or speak solely in English one day, and "foreign" the next day.

I'm not sure which is best, but I'm looking forward to finding out :)