Thank you for your answers. I realize now they were visiting females, but I was used to a hack that made pregnancy possible for visitors or young adults. I wonder what it was...
Inteen will let YAs get pregnant - not sure about JenFlowers Woohoo (both at
http://www.insimenator.net/). You can always use something like Insim or Merola's mind control mirror to make a sim selectable. Just don't make a townie or NPC selectable and pregnant unless you want some problems (ok to do if you "move them in" after they get pregnant).