Author John Irving doubted his novel, "A Prayer for Owen Meany", could ever be turned into a film, and sold the screen rights on the condition it not be released under the same name as his book. Irving himself provided the name Simon Birch for the producers to use in place of Owen Meany.
In the scene where both boys are in the school, just before breaking in Father's office, the dog is licking Simon's glasses, this leaves a wet smeared mark. In the next shot, the glasses are clear again.
As the bus heads down the hill towards the lake we see Simon with his glasses on - then there is a close-up of him without his glasses, then as the bus hits the water he's wearing them again and they fly off and hit the floor.
When Rebecca Wenteworth is walking towards the baseball diamond, she is looking behind her and waving. When she gets hit in the head with the ball, it's on the wrong side of the face. She should have been hit on the left side of the face.
John Irving praised the screening of Simon Birch but ensured the title change (from A Prayer for Owen Meany to Simon Birch) because it did not directly follow the novel.Source: http://edition.cnn.com/SHOWBIZ/News/9809/03/showbuzz/#story3