Actors Chris Pratt and Chris Evans stunned patients at Seattle Children's Hospital in Washington on Saturday (07Mar15) by turning up for a surprise visit.

The stars posed for photographs with the youngsters, signed autographs and met with the patient's families.

Evans went dressed as his on-screen superhero Captain America in a bid to cheer the youngsters up.

Later that day he wrote on, "Amazing day at @seattlechildren (with Chris Pratt). Met some true super heroes! Feeling inspired, blessed, touched. Thank you w (with) all my heart."

A statement released by patient Oskar Beechum's mother Kelli reads, "Meeting them was a nice reprieve for us. So many of our visitors are doctors, and the conversations are medical. I can't wait to watch the Captain America movie with Oskar. It will be like he knows him personally now."

The visit comes a month after Pratt made good on his Super Bowl bet against Evans to dress up as his Guardians of the Galaxy character Star-Lord during a visit to a children's cancer facility in Boston, Massachusetts.