"Oh you're so cute," Sadie wails as she hugs Carson. "I love your little smiles. Oh my gosh, I want him to stay little!"

Also, Sadie really, really doesn't want to "die when she is a hundred."

The video was posted by Alex Miller, Sadie's uncle. He told ABC News that Sadie has "a flair for anything dramatic." The Phoenix, Arizona, family also has a 3-year-old daughter named Brooklyn, but it's unclear how she feels about Carson's growing up.

"Sadie has had kind of a naive understanding of growing up and getting old (we're still not sure where she got the concept of dying at the age of 100) from an early age," Sadie's dad, Ryan said via an email sent from the uncle. "She's cried about not wanting to get older herself in the past, but this was the first time she was upset about her brother. The funny thing is that this was totally out of the blue -- we have no idea what prompted it."

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