One triplet not aging up with others

[Janna]

I have noticed that when my sims have triplets, one of them doesn't age up with the others, he or she is usually one day but sometimes two days later in aging up.

Is that common?  I generally aim for twins, if I go for more than one baby, so triplets I go for when I seed a family for project stories. 

Since I don't play the families I didn't realize it was happening until my sim families kids would attend school with the seeded family and I would see two of the kids as teen and one of them still as a child.  One or two days later that one would show up as teen. 

[Wai]

Janna, sorry, this is quite common.  The only way to ensure that they all age up together is to have three birthday parties, which takes most of the day, or to use the cheats to force aging.

[Pam]

Wai is correct.  This is very common and even happens with twins.  The game somehow loses track of how old the Sims are and they end up aging up on different days.

[Janna]

Thanks for the info.  When my sims have had twins I generally have a party, even if it is just family so I guess that is why I, so far, have never had it happen.