Chris Pratt -- PAYS UP SUPER BOWL BET ... Hey Kids, It's Star-Lord!

Chris Pratt is like a Lannister ... he always pays his debts -- and today, the "Guardians of the Galaxy" star dressed up as Star-Lord to make good on his Super Bowl wager with Chris Evans.

You already know the bet ... Star-Lord (Seahawks fan) and Captain America (Pats fan) agreed to visit the other actor's charity in costume if their team lost the big game.

Well, today it happened ... with Pratt -- in character -- hangin' with kids from Christopher's Haven in Boston ... an organization that helps provide housing for families with children fighting pediatric cancer.

Don't worry, Evans was there the whole time to follow Pratt around with a Tom Brady jersey.

And the story gets better ... because Evans says he'll be visiting Pratt's charity too -- a Seattle Children's Hospital.