Originally, Rance had no contraception spell on him, nor did he use any other form of contraception. He was basically saved by luck and convenience for a long time.
Using the personal timeline for Rance on the Alicesoft wikia, we have the following pregnancy related events for Rance:
This last event is worth saying more about, in particular. Rance was not aware that Ferris had gotten pregnant and had a child before Dark Rance showed up, nor did he know that there were severe consequences for Ferris as a result. This is when Rance actually took pregnancy completely seriously, leading him to have Sill place a contraception spell on him.
For the sake of clarity, it may be worth noting that Devil children grow up much faster than human ones. Dark Rance was somewhere around the equivalent of an 8 year old when he shows up to Rance, despite having been conceived at most two years ago.
At this point we can note he has one child, and impregnated at least one other woman (who ended up having an abortion). He's not done yet, of course.
LP0005 22 years old
- Hotspring trip to JAPAN. Had a chance meeting with Oda Nobunaga, became fast friends, and become the hidden ruler of the Oda House.
- Rangi was born.
Yamamoto Rangi is the son of Yamamoto Isoroku and Rance. As the alicesoft wikia link notes, it is not clearly stated what allowed Isoroku to become impregnated, as Sill and the contraception spell are still active during the time period Isoroku would have had sex with Rance. In Isoroku's own route, Rance specifically orders Sill to remove the contraception spell so that Isoroku may bear his son (she joined him specifically under the condition that he would give her a son to continue her family line). However, this is a side route and not the "canonical" route that subsequent games would use. Nevertheless, Rangi is referenced in subsequent materials, leading to the various conjectures on the wikia about how Rance managed to get her pregnant. I'll note that Rance also has a son with Isoroku, under the same pretenses, in the What-If game Kichikuou Rance (Savage King Rance).
But Rance is still not done, especially since after his JAPAN trip Sill has been encased in ice and the contraception spell is no longer in effect.
- LP0006 23 years old
- Incident at Kalar forest. Resulting Rance being cursed by Pastel Kalar.
- Reset Kalar was born.
The curse is because Rance raped Pastel Kalar. Pastel soon after gave birth to Reset Kalar. Reset is also born to Rance and Pastel in Kichikuou Rance, though in that game the sex was consensual and for the sole purpose of procreation. Seriously. Kalars also age much faster than humans.
This is the most recent child Rance has had so far. It is unclear if he will have more.