Slightly different situation here since the OP does not yet have citizenship, but is applying for citizenship. It’s splitting hairs, though, and I agree that having used marijuana more than 20 years ago likely will not impact his/her application.
If you answer “yes” to any of the items you will be given the opportunity to explain the crime. Having used marijuana once more than 20 years ago is not going to raise an eyebrow considering it’s legal in half the states. However, falsifying your application may have dire consequences for you and your citizenship application. I think you know the answer.
Both are major life decisions, child and immigration. If you wait with having a child there's a strong chance you will not be able to conceive. Having a child before you actually travel may add a delay to the process, but you'll still be able to get the visa. That way you have both a child and your visa. Don't wait with having the child.