The cute picture shows the five-year-olds dressed in matching green shirts and jeans with pirate hats while clutching toy guns. Both boys had eye patches and fake beards inked onto their faces and had serious expressions as they played in character.
Celine Dion dressed her sons as pirates for Halloween
"Nelson and Eddy's dress rehearsal for Halloween night," Celine wrote.
The image came after Celine made her Instagram debut with a photo of herself in the recording studio, writing: "Hello Instagram! #firstselfie".
Celine's sweet snap of her sons comes just two weeks after she took the boys to celebrate their fifth birthdays at Disneyland in California. The mum-of-three took some time off from her Las Vegas residency for the fun day out, where they enjoyed some time on the rides and met much-loved character Mickey Mouse.
Celine Dion took her sons to Disneyland for their fifth birthdays in October
The 47-year-old is trying to maintain a sense of normality for her boys following her husband René Angelil's throat cancer diagnosis in December 2013. It is the second time the music manager has battled cancer, but sadly this time it appears René is fighting for his life.
The battle has clearly hit Celine hard, and she has admitted to USA Today that although it has been difficult for their 14-year-old son René-Charles too see his father in poor health, the twins "don't know their father in any other state".
The My Heart Will Go On singer recently returned to her Las Vegas residency following a year off to care for her ailing husband, and has paid tribute to René by sharing home videos of her family while she performed at The Colosseum at Caesars Palace.