How old are the children? What was the agreement regarding religion prior to having children?
In my opinion, the children should be exposed to many different forms of faith. His, yours, other peoples'. In the end they will make their own choices when they are old enough.
I think if you were to sit in on the Bible studies he wants to do, at least you would be able to talk about your particular beliefs or lack of beliefs. The most important thing is tolerance, regardless of "religious" choices. Don't make this into a huge deal - it's just another aspect of a well-rounded education. It will be okay if the kids see that "religion" can be a little nutty sometimes.
I was taken to many different churches and exposed to many different faiths as a child. I was able to take what I needed and leave the rest - but then, no one tried to force me - that would not have gone well at all. If your husband becomes controlling around this, the kids are going to be turned off. Love and tolerance.