Here is a little trick I use.
In the marriage place field, I enter the location as *never married*. This shows up on all the reports and will transfer in a GEDCOM to other software programs. By putting the asterisk in front of the phrase, it always shows up at the top of the place master list and I just click "ignore" for this location when I do my location clean-ups. I can also use this "location" to quickly locate everyone in the tree listed as never married just by running a location report. It is a simple work-around without getting into creating custom facts that may get lost in a gedcom transfer.
I agree with the other posts about being careful about listing anyone over the age of 12 as having no children. I had a 7th great-grandmother who was married at 11 and having children at 12 (it was the early 1600's and a political marriage). I have also done a lot of cemetery indexing and find many infant graves for children who were born and died between census years and before formal birth records were created. The tombstone is often the only record that these children ever existed. If you want to document no children, you can use the same trick with a location called *never married, no children*