My older one started preschool at 2.5 years old. Before that, she didn't know much English, we taughter her "pee" and "poo" one week before the school started because we were on the waiting list and got the opening pretty surprisely.
I don't remember she had any problem catching up with English. It was very quick and smooth. We parents still speak Chinese at home, 90% of the time, till now, and my older speaks Chinese with us, 75% of the time, my younger one, 50% of the time.
Oh, I did read her books in English during night story time. I did this to both of my kids every day till they were 6,7 years old. A very good bonding, and maybe helpful for their beginning English.
BTW, we watch very little TV, but I bought them tons of books.