We've had some mixed experiences with children on airplanes. Sometimes the kids are perfect adults, ready to fly, not making a fuss, and generally happy throughout the flight (although a lot of adults aren't generally happy, so...). Other times, the kids are little monsters who cry and scream and make rude comments about other passengers. But thankfully for the person who posted this picture, they got the first type on this flight.
The kid in question here is having a blast on this flight and just playing with his toy fish. He's having so much fun, in fact, that he wants to share his joy with the people in the row behind him.