Re: How does my Baby grow up? How long does it take?

Usually it takes about a day for a baby to age up to toddler. Every once in a while it take a bit longer. The trick is to do the activity events with the child, when they appear, as soon as possible. If you don't act on that pink bubble fast, it'll disappear and then you won't get all the stars for the "good upbringing" heirloom. It may very well be that doing those interactions triggers the age-up process. 

Unfortunately, our sim parents are not able to hold and care for the babies/toddlers/children unless they're doing one of those good upbringing events, and the high chair is purely decoration. The potty seat has child interactions, though. 

Hope this helps.