Facebook Messenger just rolled out a new feature called Instant Video. They describe it in this here way.
So... it's not massively different to just having a video chat except it takes place at the same time as texting. It might even be considered more distracting.
Anyway if you're both on the same platform (Android or iOS) with the latest version of the app you should see the new video icon pulsing away at the top of the screen. Just touch it to share something instantly and have it float over the conversation.
There are shades of Snapchats quick video messaging service here but the internet is all about borrowing ideas these days. We couldn't get the latest version of the app yet on Android in Ireland so it should be rolling around soon.