Hollywood stars Johny Depp and Robert Downey Jr shine their limelight to sick children who are most in need of a smile.

Depp, who plays the charismatic but often treacherous Captain Jack Sparrow in the hit movie franchise Pirates Of The Caribbean, channeled his character's softer side as he took time out from filming the latest installment, Dead Men Tell No Tales, to visit poorly children in hospital, reports the daily mail.

The Hollywood star turned up at the Lady Cilento Children's Hospital in Brisbane, Queensland, in full costume after a busy day filming scenes on the Gold Coast set.

The surprise visit delighted the young patients at the hospital, which treats newborns and children up to 16 years of age.

Many posed for selfies with the 52-year-old actor who admitted he often travels with his Captain Jack Sparrow costume for when he makes impromptu visits.

In a series of sweet snaps of the star's hospital tour, Depp can be seen chatting to young fans and giving some hugs.

The images were taken by Juiced TV - a show made by the children being treated at Lady Cilento Children's Hospital.

The 30-minute weekly kids TV show often features interviews with celebrities who visit and Depp appeared to be answering questions from the patients in some of the images.

His visit comes after several busy days of filming on a Gold Coast beach set, which features a huge prop of Captain Jack Sparrow's ship.

The star was spotted on set just a few hours before his hospital visit and appeared to be in good spirits as he smiled and chatted with the cast. 

Meanwhile, Actor Robert Downey Jr., who plays Iron Man in the "Iron Man" and "Avengers" movies, has partnered with a maker of bionic limbs to give one lucky 7-year-old an amazing new arm.

Alex, whom RDJ calls the "most dapper 7-year-old [he's] ever met," loves superheroes and riding his bike, and was born with a partially developed right arm.

To give Alex a new arm, RDJ teamed with Albert Manero, a Fulbright scholar and doctoral student in mechanical engineering at the University of Central Florida who builds and donates low-cost 3D-printed bionic limbs to kids around the world through his volunteer group Limbitless Solutions, reports CNET.

The arm cost just $350 (about £235, AU$455) in materials to make, as noted by Microsoft’s The Collective Project, which is featuring stories of students making positive changes for their communities. That makes it far cheaper than the $40,000 (about £26,900, AU$52,000) it traditionally costs to make such limbs.

Check out the video at the top of this post to see RDJ presenting a grinning Alex in a red bow tie with his new arm, and be sure to have a few tissues at the ready. Then click on the various links throughout this post to learn much more about this incredible project.