Ivanka Trump's daughter Arabella sings to her baby brother Theodore in new video

It looks like Arabella Kushner has this big sister thing under control! Ivanka Trump and Jared Kushner's four-year-old daughter shared a precious moment with her newest brother. In a video posted on Ivanka's Instagram, Arabella sings a sweet song for her just days-old brother, Theodore.

Arabella serenading her new baby brother. 

A video posted by Ivanka Trump (@ivankatrump) on Apr 4, 2016 at 1:08pm PDT

"Arabella serenading her new baby brother," Ivanka captioned the adorable video. In the clip their daughter is seen holding Theo while she sings Twinkle, Twinkle Little Star. At one point Donald Trump's youngest grandson starts squirming, but his big sister remains calm and keeps her performance going.

The businesswoman is not shy about sharing her family's sweetest moments. On Monday, the new mommy shared a video of her husband Jared and their two-year-old son Joseph introducing Theo into the boys' club.

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"Sweet moments with baby Theo," she captioned the picture on her Instagram, that shows Jared and Joseph gazing into little Theo's bassinet.

Since little Theo's arrival on March 27, the Kushner clan has been beaming over the new bundle. Ivanka shared a glimpse at a moment between big sister Arabella, proud papa, Jared and Theo after his arrival. "This is love #bliss," she captioned the picture of a sleeping Theo being held by his father while Arabella stands behind him.

Ivanka can always count on her family to bring the aww-worthy moments.