I think it's important to give my children some sort of spiritual foundation. They will be free to make whatever choice they want, but I do believe it is my responsibility to tell/show them what I believe and why.
I also think it's important that both parents are firm in what they believe and don't change every other week, whether they think the same things or not. Change to kids is scary a lot of the time, especially spiritual issues, which they may not understand completely for the first couple of years.
I was raised in a Christian church, but it was slightly different than other typical Christian churches. We didn't baptise, or have communion. There were a couple other things as well. In fact, I spent most of my life being told I wasn't really "saved" by other more traditional Christians.
I went to public school, and none of my friends there were Christian. So I was familiar with other faiths besides my own from a pretty young age.
Dh was raised Christian, but his father changed churches according to his financial needs, or if he was trying to find a wife, and he spent a lot of time bouncing back and forth between places. He also had friends of other faiths.
Regardless of the firm spiritual foundations both dh and I had, our high school and college years raised a lot of questions, for both of us. My mom freaked out, my dad was more understanding. And because of his understanding and permissiveness to have questions, I went in a great big circle, but came back to what I believed as a child.
Dh's father freaked out as well, when dh started questioning things, but dh is the strongest person I know, spiritually, and he found his own way as well, support or not.
In the end, what dh and I believe is not exactly like either of our parents. And that's okay. We don't even agree on everything among ourselves. But we have the same basics, and that's the part we'll try to teach the kids.
For me, I think the main thing is to let the kids know they have the freedom to choose, and not to use any kind of religious thought or spiritual thing as a weapon to try to force or scare them into believing a certain thing.
I want them to look at religion/spiritual things in a positive way.