As for our son, we continue to use the same model. At age 2 he started to read logos, now at 3, he can understand Spanish mostly, and uses English to answer grandma's questions over Skype (not that she is happy about it! Well, perhaps she is!). The most important thing for him is to be ready for pre-school and here is when our series of books will play a very important role. The contents aim to get a child ready for pre-school, whether they are native speakers of English or coming from a family with parents that speak a different language, challenged to learn two languages at the same time.
A few words about Bringing up bilingual children...
Whetheryour children are American citizens or not, they are now part of an educational system in a different language. In order for them to be successful learners, why not encouraging them to learn it at home as they are learning your family's mother tongue. Many will oppose to my thought, however, I speak by my personal experience. My husband and I decided that encouraging the use of English would be beneficial for our daughter, and here she is, finishing elementary school as a straight A's student, spotted as a gifted child and published her first book with mom at the age of 10!
True it is, her Spanish had to suffer a bit. She can now understand mostly, as well as speak it, not the way grandpa and grandma would have liked, though. Now that her English is good enough, it is time to catch up on the other one. I believe, though, she'll also have time to time to polish it during her college years (as long as her basis are there).