You just need to prove that you are legally married to an individual who is a US citizen or who is being granted a green card to get a green card. They will ask you to provide evidences to prove that your marriage is bonafide. The following documents will be helpful for that: evidence of joint residence, joint health insurance, joint ownership of a property, joint bank account, joint tax return and parenting a child together. Not all the evidences listed above are required. Having a kid together is one of the evidence that will help you prove your mariage is bonafide. It does not mean that you can not prove a bonafide marriage without having a kid together.

I hope this helps to clarify your question.