For a moment, the girls puzzle over the iced cookie cakes which read 'Big sister' ('Big sister again' for the older girl). But it doesn't take long before a shriek of joy makes it clear that the pair have understood mum's message.
As is always the case with brilliant news, their initial reaction is disbelief. "Really?" they repeat, hesitating for an instant before mum's confirmation sends the younger girl rushing in for a cuddle.
When all the noise subsides, it seems like they have got over their initial excitement. But when the mum asks: "Do you want to see picture of the baby?", it unleashes another wave of feverish screaming.
"You went without telling us?!" the older girl cries, before both huddle round to take a peek at the ultrasound snap. Once they've worked out which way up it goes, the pair are visibly moved by the thought of a new sibling.
"You're going to be a big sister!" the older girl says, throwing her arms around her younger sibling.
Happy as she is, the little girl clearly doesn't fully get the whole pregnancy thing yet. "So it's gonna be a year before it's born?"
Mum and dad better keep this video handy in years to come - we reckon there'll be some moments when the girls need to be reminded that they were once so happy about having a third sibling!
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