Well, playing nonstop for multiple births is what makes it not necessary to roll. Basically, there's a list - 1, 2, 3, 4, etc. Every time you restart the game, the first baby born fits profile 1 - what that profile is specifically depends on the parents, so if you have baby 1 in one household and next time it's in another household, you won't notice a problem. And if you keep playing, the second kid will be 2, the third 3, etc. The problem is when you play through one birth, save, quit, and next time go back to that house and have one birth without rolling the dice. It's why twins are never 100% identical, though they can be quite similar - they're automatically 1 and 2 on the list or later on if you've had other kids. So playing nonstop through many births will solve the issue, as will rolling the dice - which sends you to a random number on the list, so you might start that session at 15 and the next at 9 on the list.