Continuity mistake: After the pool incident when David is writing letters. Monica is looking over the letters that David has written. There's a point where you can see that she's still holding at least 2-3 sheets of paper but when the camera shifts back to the writing there's only one in her hand. There should be more than one paper in her hand. And when viewed from behind her back the sheets are neatly lying on top of each other, when seen from the front, the sheets are tilted.
Continuity mistake: When Monica first meets David, David walks out onto the carpeted floor and takes a step down to the wood tiled floor. He taps his feet on the wood tiled floor and then steps back up to the carpeted floor. He taps his feet again and turns around to face Monica. This is just before he tells her, "I like your floor." The mistake here is that Monica was pulled from the carpeted floor to the wood tiled floor before David walked in. So, David should not have had to turn around to face her because she would have been in front of him ... not behind him.
Continuity mistake: They show David staring at the silver dancers dangling above his bed in which he sees his reflection. Next shot shows him down too low to be seeing his reflection. Also, there is a sound of a wind chime, however the silver dancers are not touching to make the sound.
Continuity mistake: When the robot catcher nets in the stray robots including David they go in the cage of the moon balloon, where David is struggling to hold on to Teddy as the balloon rises into the air. Teddy says "l'll break David" and at that point Teddy slips through Davids fingers and falls to the forest floor. Teddy then immediately runs to the top of the hill where the balloon he just fell from has already sunk well behind that hill only just seconds after falling from it. The balloon has moved far too quickly.