I think what idapop is referring to is getting families, or females, pregnant so when your sim has offspring there will be mates available.
I don't think there is a lifetime reward.
What I do to seed a town is go in before I start the game and visit several families and have the women become pregnant (I stick to married ones, but that is a personal aspect for me). When you go to return to game and chose to create your family or use a townie one, there will be several families with pregnant women. However many you want to get pregnant, that will now be expecting and more children in the town.
Another thing I have done is raise the kids in the families to teen (use the cheat for aging up or birthday cake) and save them. When my kids are teens and need to find mates, if the family has moved out, I can just replace them.
Did that because I had a couple of the families move out after I had seeded them, there went my kids future mates.
I give them random traits, unless they have neurotic, mean and I can't remember the third one
.
I have given the parents the LTR points for the fertility reward, to insure pregnancy, there is a cheat for that.
Got the idea from another forum member who told about doing that in a project story for a town that didn't have kids. Now use it a lot in a town that doesn't have very many kids. I didn't come up with the idea she did, just can't remember who it was.