Dellena,
I don't use mods, but, I have found another way of getting a baby boom. Start a town, any town, you won't be saving the game. Select all the couples in the town you like the look of. Each household in turn: Start playing the family until you can afford fertility treatment. I don't need to explain the next step
. Exit the household, Evict the couple and save to bin. Repeat until you have enough pregnant couples. Exit game.
Now, every time the game looks as if it needs some new blood, take one family from the bin and place them into an empty house using edit town. You don't need to do anything with the family after this. Twins and triplets, not your own, are so cute.
. (Not to be used in challenges etc.). (You could do this more quickly using cheats to get the fertility treatment too.)