不说.

Instead,

"A good job. We're proud of you. You should be proud of yourself."

Agree with your point.

That kind of saying diminishes the child's effort, limits the meaning of the win, and worse, tells the child his "self" is nothing without someone else's idea of a "collective". No wonder many Chinese kids lack the self once they leave home when that is called for in a society where individualism trumps collectivism.