A Gold Star was a common reward when I was a child (long ago), and I imagine it still is. If I remember, we were awarded silver stars and maybe other colors for lesser accomplishments and gold stars signified multiple lesser accomplishments. (5 silver stars converted into 1 gold star).
If the children are all boys, something like a military rank might work. I don't know if there is something equivalent for girls or for mixed groups.
I think we received more tangible rewards at some point after reaching some goal. Being appointed a new role or responsibility or being called a leader (which actually had a job description) were some of the rewards.
The main difference is in how formal it comes across.
"Kudos" is considered a 'real' word while "props" is considered slang but neither are very formal.https://www.etymonline.com/word/kudos
"Kudos", usually used as an interjection like 'congratulations', comes from UK university slang, which means by now it is fairly formal. For example:
Kudos! Your excellent presentation to the CEO will really have you climbing the org chart!
"Props", short for 'proper respects', comes from US hip hop slang, so it is more easily recognized there than in the UK.
Gotta give props to that kid for that stunt. When does he get out of the hospital?
As someone on reddit said:
"Props is for friends, kudos is for work."
Best Answer
It never occurred to me to use these words in the same way. (Although some do.) One would "give kudos" (like offering congratulations) on/for a job well done. *Bravo, or brava, is almost always used to laud a performance of some kind. (Including falling down an entire flight of stairs and landing on one's feet, or even having a baby.)
"Kudos," is more of an affirmation, while "Bravo!"/"Brava!" is always an exclamation.