Three final learnings

Yesterday I finished this book: How Languages Are Learned and here are the last pieces of information I learned from it:

1. That the best time to have my child srart learning a second language is around the age of 10 when (s)he has already improved gramatically in his/her first language. The question is considering that my husband and I speak persian as our first language living in a country where the first language of people is English; which language would be my child's first?
2. That teachers like parents tend to change the structure of their spoken language intuitively according to the progress their students make in learning the second language. To me, that was an interesting finding.
3. That when teaching a second language, especially in the immersion contexts, teacher's correction of students' errors in the form of "recasts" often is received unnoticed and as part of the conversation. So the teachers should grab the students' attention by indicating directly before the correction what they are going to do; like the following suggested interaction: "I understand what you say, but here is how you can say it better...".