Christians: is it a sin if we do not want to have children even though we are married?

It's not. I was married for fifteen years and we never had children. He died two years ago.

None of our friends at our church accused us of sinning.

Some people also cannot have children. It's not a sin to marry for love.

No it is not a sin for a Married couple to not want to have children. I know of a few Christian couples who did not wish to have kids. It is a sin however if you are using contraceptives such as condoms or birth control, if you "fixed", If you have an abortion, etc. Your married so have sex all you want but if you get pregnant know that it is Gods will that this Child be born and if you can not afford the child give it up for adoption. There are plenty of parents who want children.

God wanted humanity to be fruitful and multiply, which humanity as already done. It's not a command for every single human being. If it was, both Jesus and Paul would have lied when they each said some people are called to be celibate.

You aren't required to have kids. Probably the toughest requirement is in the Catholic Church, which requires that you "accept children" as God sends them to you. (That's why they don't like artificial birth control, but even they promote and allow "Natural Family Planning".) If it turns out you can't have kids, well you can't have kids, nothing wrong with that.

I'm a single Dad with two kids, and I love my kids more than anything, so it's my PERSONAL opinion that someone who actually wants a "child free" life is pretty selfish and a bit of a materialistic butthole. Being a selfish materialistic butthole is not conducive to a good Christian life, but it's not a sin, in and of itself.

If it isn't a sin not to have children then there goes one of the major objections to gay marriage. Either it is a sin or the anti-gay Christians are hypocrites.

There are already too many people in the world.

no - it is a personal concern between you and your spouse

Not at all, your choice.