Revealing mistake: Just outside the hideout's tree entrance, the pirates carry Wendy, her brothers and the Lost Boys away. When Michael is thrown over a pirate's shoulders, Freddie Popplewell's (Michael) spandex shorts are perfectly visible. (01:10:20)
Revealing mistake: When Peter is trapped in the net underwater at the Black Castle, it's plainly visible that where he cuts on the rope is pre-cut already. (00:50:05)
Revealing mistake: When Michael whacks the pirate in his groin, he bends over wincing in pain with his mouth open, in the next shot, though the pirate is bent over, his facial expression is completely different and is not in any discomfort. He does however stand at the ready for John's blow, which actually never even touches him, and the pirate's head starts to fly back after John's hands pass him. (00:48:45)
Revealing mistake: Michael and Smee are on the gang plank of the Jolly Roger, in the shot looking up as Smee jumps, Michael's arm partially disappears in front of the sail in the background. (00:24:50)
Answer: It's not that you never age, it's that you never grow up, i.e. pass into puberty and become an adult.
Myridon