Most of the childless couples are indeed happier than those married couples who have children.
Children can really get on your nerves at times and cause fights between spouses and even me and my wife fight at times due to our kids and at first we thought we would be much happier if we never had kids.
But overtime we grew to love our kids and even though we fight about it sometimes because the kids can drive us crazy we still love the kids and we still love each other as well.
Yes you can be happy without having children and many people do live a happy life and have a happy marriage even when they have no children.
Children can either make your life happy or make your life a living hell and not everyone is meant to be parents and that's okay.
Children are a huge responsibility and you should only have children if you're absolutely ready for them and can support them financially because kids are expensive.
Although for some people having kids is worth it and they can be a joy but you have to be prepared for tantrums, caring for them etc.
Some people regret having children and other people don't regret having children.
I have 3 kids myself and my life is much better because of them but for some people it may not be that way.