Agree with the 'not fluent by Christmas' comments. My kids were 4 and 8 when they went into French-speaking Swiss schools. I have reasonably fluent French so was able to follow along with their progress; in my experience of watching foreign kids come through our school, many of the 'gosh, they're fluent already!' comments came from parents with little or no French themselves, who mistook a few stock playground phrases and a good accent for bilingualism.
My youngest hardly spoke for the first year, but after the second year she was fluent for her age, with a fabulous local rolling Vaudois accent. 6 year olds don't really need much vocabulary for school. My oldest was conversationally fluent after 18-24 months, as in he didn't sound foreign ALL the time like in the early days. But even after 3 years, he was still making errors of gender, and using obvious (to me - I did the same) workarounds for vocabulary gaps. He could, however, use the subjunctive without even knowing he was :)
I've read that it takes 3-5 years for kids to acquire something like native fluency, and even then their vocabulary will be lacking in non-school/ non-kid situations, as they're usually missing out on everyday adult conversational input. This matches my experience. The best I ever saw for speed of acquisition was a 10 year old girl who was fantastically bright, very social, highly committed and extremely studious; she worked really hard on the language and, by the end of the year, could have not-too-stilted conversations with her friends on a range of topics suitable to 11 year olds rather than sounding like a child some years younger.
My go-to rough test for fluency is to be able to render into foreign the following: you see a poster for a circus, but it was for last week and you've missed it. If you can say 'Oh, what a shame - I would have liked to have seen that,' then you're well on the way!
But take heart, OP - even though it took much longer for fluency than I'd been led to believe, my kids were perfectly happy throughout. They very quickly picked up enough French to follow playground games, and were very much welcomed by the other kids as amusing novelties.