Steve Irwin's children, Bindi and Robert, pay tribute on his birthday

Feb. 22 (UPI) -- Celebrity siblings Bindi and Robert Irwin are honoring their late dad, Steve Irwin, on his birthday.

Bindi, 20, and Robert, 15, paid tribute to the Crocodile Hunter star Friday on what would have been his 57th birthday. Steve Irwin died at age 44 in September 2006.

Bindi shared a throwback photo of herself with her father at the Australia Zoo. The picture shows Steve smiling while holding a baby Bindi and a koala.

"Thank you for always being my guiding light," Bindi captioned the post, adding a heart emoji.

Robert thanked Google in a post on his own account for featuring Steve in a new Google Doodle. He remembered his dad as someone who strove to make the world a better place.

"Thank you so much, @google for honouring dad with his own #GoogleDoodle all over the world. A perfect way to celebrate his birthday, sharing everything he did to make the world a better place," the star wrote.

The sibling star with their mom, Terri Irwin, on the Animal Planet series Crikey! It's the Irwins. Robert announced in January the show was picked up for a second season.

The show follows the family as they live and work at the Australia Zoo. Bindi promised in February 2018 to uphold her dad's legacy with the new show.