Could Uncle Owen and Aunt Beru have children?

Question

At least in canon, there doesn't seem to be any evidence that Owen Lars and Beru Whitesun had biological offspring of their own.

They are a more or less traditional, married, farming couple (albeit moisture farming). Given the many duties that we see Luke performing in A New Hope, it seems that they could use all the help they can get, and — if you compare to farming communities on Earth — one way to get that help is by having a large family. Granted, they did have many droids as @Himarm points out in comments, and so that might replace the need for people. Also, more mouths to feed out in the desert may not be a good thing, as @terdon mentions.

Still, all of this raises a question:

Were Owen and Beru capable of conceiving? If so, did they make a conscious decision to have no children of their own apart from raising Luke?

Answer 1

They were unable to have children.

According to Lucas Books' The Official Starships & Vehicles Collection #3, Owen and Beru weren't able to have a family of their own.

In the dark days that followed, the fall of the Republic seemed distant to Owen and Beru on dusty Tatooine. Then one of the last of the harried Jedi, Obi-Wan Kenobi, delivered a child to Owen and Beru. This was their nephew, Luke, secret son of the fallen Anakin. Unable to have a family of their own, Owen and Beru were content.

Luke's foster parents provided a loving home, but they were haunted by the spectre of Anakin. Owen could not stop Luke from showing traits that he had seen in Anakin.

This has since been backed up in the (canon) Star Wars: From a Certain Point of View short story Beru Whitesun Lars.

It’s not as if I wasn’t expecting it [thought Beru]. The day Ben Kenobi put that little baby in my arms was both the best and worst day of my life. Best because Owen and I couldn’t have a child of our own, and suddenly we did.

...

I won’t lie to you—I thought about it. Especially right before Luke came along, when Owen and I had just found out we’d never be able to have kids of our own. Our only resort was to start seeing one of those fancy fertility droids in Mos Eisley. It almost didn’t seem worth it, though, when you consider what Mos Eisley was like back in those days.

Answer 2

While the points about having kids may be relevant, but given how much physical property the Lars' had, not land but droids, landspeeders, evaporators, and what not, I have doubts that they were stuck on Tatooine. Luke owned a fancy (for Tatooine) landspeeder and a T-16 Skyhopper, and was able to save enough money to afford them, and parts to repair them. I'd say the Lars' could have afford a ticket to a easier world, but with no capital once they got there.

I always thought it was a combination of other factors, very few of them biological:

1. Before getting married, they both met Anakin Skywalker, and probably had a good idea that he had something to do with that slaughter of the sand people. That would affect my thinking if I was in any way, shape, or form, related to him.

2. As a young couple, potentially thinking about having children, some guy named Kenobi showed up and handed them a baby and said, "This is your nephew, raise him." Had I been in a similar situation, explanations would have been forth coming. The explanation that Anakin Skywalker is Darth Vader, could have killed any desire to have children.

3. Being given a newborn with that they have no emotional connection with could have killed and desire to do the newborn stuff with your own children. Plus by raising your nephew, they could check the "I done good" box on the life accomplishment checklist, without all the hassle of pregnancies.

However, there are some other things:

4. According the the Complete Locations book published by DK, Owen and Beru slept in side by side twin beds, like 1950s TV couples, which could have put a damper on things. In contrast, Amidala is shown in the Cross Sections books have beds large enough to sleep four on starships.

5. Having Luke have no close relatives makes it easier for him to to leave his home and fulfill his mythic hero role. Similar things happen to several other characters (Han Solo, Wedge Antilles, Corran Horn, Iella Wesseri, and anyone from Alderaan.)

6. George Lucas would have learned a lot, if not most, of his craft from people who lived through the Production Code Era and may have that a general sense of conservatism was needed to get an oddball project off the ground.

7. The plot required it.