I FIGURED IT OUT!
So basically, I had believed that if you had a toddler sim that won't age up, it was a bug that was un-fixable and you had to delete the child before the bug spread. But I discovered that there is another way.
My girl toddler sim wouldn't age up, so I sorrowfully deleted her. Later on, I felt bad that there wasn't any memories of her in the house. So, I closed down the game without saving, to when she was alive. I made a bunch of paintings of her before her birthday and put them in the house. And when her birthday came, I double checked to see if she still wouldn't age up. But guess what? SHE DID! The virus was gone just by simply CLOSING DOWN THE GAME WITHOUT SAVING!
Now, I don't know if the amount of time before her birthday you have to go back counts or not, but It was around a week that I had gone back in time.
Hopefully this will help you with further problems!
*Remember, if you save after you have celebrated her birthday, you will have to delete her!!