You teach the French reading / writing by getting your husband to read in French every day. Then when your son is older, you add the writing. It's not hard and not a big deal. Our kids have no formal English and they learned informally. Reading / writing skills can transfer from one language to another. My 8 year old is doing fine now in English, my other 2 I'd dare to say are above their peers in the UK in English.
My son is English-French bilingual. We live in a country where the main language is English/Arabic. He has been attending a French nursery since he was 10 months old. He will be 4 in Sept and starts an English language IB school (Arabic and Spanish will also be taught) . He will also have additional Arabic after school. Home language is English. DH speaks close to fluent French, mine is okish.
DS will continue to go to his nursery after school but there isn't any teaching per se. His oral will be fine but he needs to learn to read and write at some point. Any ideas how to deal with this?
I have a DD who will be in the same position next year so very happy to invest in necessary resources. I'm keen to avoid extra tuition if possible as he needs time to play/ be bored as well.