It works great for me.
I had 5 sims and 2 cats and the cats had 4 kittens so the total became 11. Yay!

Now one of the sims rolled a want to have 10 kids and I want to try it so I edited the userStartup.cheat file.
My question is Do I have to or should I press enter after I type/paste each line in? So that there's an empty line between them?