Animal cruelty punishment !?

It's a crime. He has no good reason for killing the seagull. Please report him to the principal. Kids watched him, so you have witness, and little kids almost never lie so you have concrete proof. Killing an animal in front of a young child is bad because the children will experience watching animal abuse at a young age and this may leave a sign to them that animals can be abused. Of course, teach them the right things afterwards.