In Chapter One, Kino kills the scorpion that stings his son and poisons him.
" He looked past the pearl, and he saw that the swilling was going out of the baby's shoulder that poison was receding from its body. Then Kino's fist closed over the pearl and his emotion broke over him. "
" My son will read and open the books, and my son will write and will know writing. And my son will make numbers, and these things will make us free because he will know - he will know and through him we will know"
" It is worth fifty thousand ," he said. " You know it. You want to cheat me."
Kino beats up his wife because she reaches out for the pearl and he's afraid she'll break it.
By the end of chapter 6, Kino ended up killing his own son on accident.