I started the 100 baby challenge in Sims 4 and my sim Skyla has 13 kids. I haven't continued the challenge yet because I am having fun with another family at the moment but the way I was playing was once the baby aged up to a kid,I would get them to an A in school as quickly as possible and from the rules I read,you can age up kids and teens as soon as they have an A in school. As soon as the teens aged to YAs I move them out.
I also would make Skyla gain a relationship with the next guy I wanted her to get with while she was pregnant. Then as soon as she would give birth I would invite the guy over and have them try for a baby. She also would get fertility massages done as well. Out of her 13 kids,I believe I had 3 sets of twins? No triplets though.
It's not an impossible challenge if you get a system going :)
