child ages faster than parent?

I'm running into a similar issue with Baby Ariel. She has not aged at all. I aged her myself to young adult so I can marry her, but she's been stuck at day one of that age group ever since. I don't do challenges so mine is different in that way at least. She has a toddler and a baby, but she shouldn't still be on day one of young adult anymore. She's stuck. Everyone else ages up. Just not her. 
I noticed that this first occurred in a old save, but thought little of it because I rarely played her, but now it's occurring again in my brand new save.