The businesswoman captured the moment of sisterly love as Arabella gave five-month-old Joseph a bear hug.
CLICK ON PHOTO TO GO TO FULL GALLERY
She followed this up with a picture of angelic-looking Arabella, two, wearing a pretty white dress and smiling sweetly at the camera.
Ivanka, 32, relishes being a family of four after welcoming her second child with businessman Jared Kushner.
"We do things together as a family. And it’s so cute to watch Arabella hold her baby brother - she is very protective," she told US publication People.
Donald Trump's daughter said she feels much more relaxed as a second time mother.
"I worried too much the first time around about how I would handle everything,' she said. "Now I know how fast these early days go by, and I want to enjoy every second. I love it."
Ivanka says older sister Arabella is very protective of her brother Joseph
As much as she loves spending time with her children, Ivanka shows no signs of giving up her multi-brand empire to be a full-time mum.
"I hate the title 'working mom' because I think every woman's a working mom by definition.
"I worked very, very hard before Arabella and there were times when I felt stressed, but once you have a child it's a whole different level.
"But really every day is just making sure I do have the right priorities and I'm doing the right thing by my family and my work as well."