How does Kino react when he sees the scorpion is about to bite Coyotito?

He leaps to grab the scorpion and kills it.

"Kino's hand leaped to catch it, but it fell past his fingers, fell on the baby's shoulder, landed and struck. Then, snarling, Kino had it, had it in his fingers, rubbing it to a paste in his hands. He threw it down and beat it into the earth floor with his fist, and Coyotito screamed with pain in his box. But Kino beat and stamped the enemy until it was only a fragment and a moist place in the dirt. His teeth were bared and fury flared in his eyes and the Song of the Enemy roared in his ears."

After this, however, he feels completely helpless. Ultimately, Juana tries to suck the poison out and Kino goes to get the doctor.