Assuming you want a working you can perform, here.
Remember, energy is a tool. Gather the proper energy of a proper color and program it to your desires and instruct it in such a way that what you want has already happened. An affirmation, if you will. For example, one way I do it.
Gather the energy of a corresponding color of the nature of my working in the form of a ball between my hands.
While envisioning what I wish to manifest, say to catch a fish, I will be straight forward and specific. "I am catching a healthy fish, fit for a meal." Or command it, others may not agree with me on this one. "Let me catch a healthy fish, fit for a meal". Some even choose to make a neat little rhyme of it.
Then I would "shoot" the ball in the direction of where I wish for it to manifest, in this case the water. In your case, your parents reproductive system or a picture of them.
The universe has a funny way of interacting with our thoughts and what we say. It's reply is always "yes". Energy, like water, travels the path of least resistance. "Yes" is not resistance. "Yes, you are catching that fish". Remember to maintain the mindset that it is/has already happened and act like it. Going after with the mindset that it hasn't happened yet will manifest that it truly hasn't happened yet. You will get "Yes, they haven't gotten pregnant yet" instead of "yes, they are pregnant".
Props are not necessary but as stated on JoS they can help with a focus point.
You can go to a Demon who works specifically on this issue and ask for assistance in the working. Some prefer to baseline go to their guardian demon, who would seek out assistance on your behalf or do it themselves. You don't have to know your GDs name. Just know they're there for you.
Before sending the energy out you can also vibrate a rune that corresponds to the nature of your working, focusing on the image of them having a child while doing so. Highly recommended, given that runes are quite powerful.
All information regarding what I've discussed can be found on JoS.
