There's nothing more adorable than a soon-to-be big brother. And you can tell by the smile on this little guy's face that he is thrilled to pieces with the news that his only-child status is expiring. As his mom's belly gets bigger and bigger, his smile gets wider and wider.
He also starts to take the older sibling thing seriously. Before our eyes, he morphs from toddler to big kid, even going so far as to swap the diaper for big-boy underpants. (Nice work, Mom!) But the reveal comes at the end, though there's a hint in the video (besides the title, we mean). You'll spot it at the 49-second mark.