Better yet, how does a father bless his sons?
Isaac didn't bless them as they were but who they hoped they were - which is very different than who a parent wants his kids to become. Jacob was chosen by God to carry the promise forward. Isaac wanted that to be Esau. He loved Esau's game-hunting, outdoorsy life. Jacob was a momma's boy.
That's who they were. But God chose to use the lesser, the weaker, the "less desirable." He does that often to make sure people understand that He's the One who does what is being done, not a group of super-talented charismatic leaders (see 1 Cor. 1.18-31). But it's in all of us to tend toward and even prefer the strong, clear, pretty, and tall. But it won't necessarily put us on God's path.
So this is how I pray for and (hopefully) bless my sons...
I affirm who they are and who they are becoming.You do the former because not every kid is a select baseball star, a GT student, or a Beethoven-in-waiting. You do the latter because Jesus is in the business of transforming kids and adults of various stripes, shapes, and sizes and the character and contours of soul is the only thing they'll take with them when He calls them Home.
I pray for attributes God wants them to have.