It's tricky. Your situation is even more complicated with kids but I did think about xmas (and birthdays, mine being in a few weeks as is his) and the impact of breaking up now. Your kids knowing what is going on is great.
I don't know if it helps but I came to the conclusion that maybe it would be better to tear off that bandaid and face the fact that xmas and the holidays will not be with him. The sooner I get used to it the better. It's going to be sad but atleast next year I can hope for it to be better. Maybe your kids will appreciate that more? Just my 2 cents.