The clip stars their one-year-old son Noah wearing bright yellow Minion pyjamas, and starts with Bublé asking: "Hey, who's that in there?"
The camera turns to Lopilato laying down with her top pulled up showing her belly.
Noah points to his mum's belly and says: "Baby!" then silently walks off. Our guess is he doesn't quite understand what's going on yet.
Subtly playing in the background is Britney Spears' Oops I Did It Again. How convenient...
The video, which was uploaded to Bublé's Facebook page with the caption: "Noah has something to tell you...", quickly garnered nearly two and a half million views.
The post was soon flooded with congratulations messages and within the more than 8,000 comments, many people praised Noah for pronouncing the word baby "so beautifully".
Another wrote: "Congratulations! Noah, you are going to be the best big brother!"
Bublé and Lopilato wed in March 2011 and Lopilato gave birth to Noah, their first child together in August 2013.