The day comes around and the menu that pops up asking if I want to adopt a baby, toddler, or child appears. When I select baby, no van pulls up. So I exited out back to the neighborhood screen to try again. Still nothing. I tried clicking on toddler and that works, but why doesn't the baby option work?

I think I only ever experienced this problem once and that was when the school bus never came.

You may have downloaded a hack accidentally and it is probably conflicting with something else. You will probably have to take out your hacks and test them.

Try following this http://www.modthesims.info/wiki.php?title=Game_Help:Game_Problem. It'll help you resolve any problem you may have.