Does anyone ever deign to speak with children on flights? I'm sure if you had politely mentioned that the recline wasnt working because your knees were there, he would have stopped.

Kids don't sleep sitting up any better than adults do. The little sister was probably laying across her mother and/or brother with the arm rests up.

Although children don't have long days at work, perhaps the parents had them up and active early so that they would sleep on the flight as not to annoy those who rank children right up there with root canals.

A little polite communication on board would have probably answered your question and educated the child as well.