The only time I've ever had more kids than planned is with alien abductions. Usually I try very hard to have just one child per family. Sometimes they'll get twins and very, very rarely triplets, but they only 'try for baby' once.
Recently though, while playing the Drifter challenge, my Drifter's elder Father was abducted and ended up giving birth to alien twins! So now I'm playing the largest family I've ever had in TS4, 8 in total which includes; my adult Drifter, her adult husband, their teen daughter, her elder Father & elder Uncle (they are twins and with normal gameplay for the challenge wouldn't be living with her, but I've been having problems with urns disappearing so moved them in), a female adult alien and the twin newborn aliens!
IF everything had gone to plan, the only Sims that should be living in this household would be my Drifter, Hubby, daughter and the alien.
The worst part? According to the rules of the challenge, I can only control my Drifter. Everyone else is on full autonomy. o.O It's certainly been the most interesting House so far in the challenge though and a lot of fun to play. My fingernails are gone and I'm bald now, but que sera sera. :D