Revealing mistake: In the beginning, Gordon is driving his truck and "drinking" something out of a thermal mug. He's be-bopping around so much it would have spilled all over him. If you look closely, you can see he's not really drinking at all.
Revealing mistake: At the beginning of the film when Gordon is delivering the mail to Spike's house, Spike gets loose and chases Gordon. Gordon runs to a tree, and somehow he flies all the way up to its branches.
Revealing mistake: While Gordon and James are in the mail truck trying to outrun the baddies, James opens the back door and starts throwing the boxes, and in the closeup we can see the knotted black safety strap attached to the boy's back for the stunt.
Revealing mistake: When Gordon falls with the broken drain pipe his yellow boxers are ripped off, but when he lands on the grass, even though we know he's supposed to be naked, we can see he's wearing white briefs in the side shot.
When Stephanie (the kid's mom) gets sprayed with mud by the bus, it is accelerating as much as it can in reverse. Why would it accelerate so much in reverse if it's trying to avoid falling down the hill?