(at around 6 mins) In Child's Play 3, the entire left side of Chucky's face was removed by a scythe. When Chucky is sewn back together in this movie, though, it's the right side of his face that is stitched back on.
(at around 6 mins) The arm that Tiffany gets out of the chest to stick on Chucky has one finger pointing while the others are closed. When it shows a shot of Chucky before cutting to David, we see that all the fingers are outstretched, yet it is not the type of hand where you can move the fingers manually.
(at around 1 mins) The flag in the beginning of the movie is improperly displayed. When hung on a wall, the Union (meaning the stars) is supposed to be in the flag's upper right corner, or the viewer's left.
The Chucky doll's body style changes throughout the movie. When he is sitting next to Tiffany in her trailer and when Damien picks him up, his legs remain in a seated position, much like a G.I. Joe, but when Damien throws him, he lays flat like his limbs are limp like a rag doll. However, considering that Charles Lee Ray is controlling the doll's body, it is plausible that he chose these positions himself because he is always part human, he is never all doll.
(at around 33 mins) The Heart of Damballa that Charles Lee Ray was supposedly wearing on the night he was gunned down wasn't actually in the original Child's Play. The newspaper clipping Chucky shows to Tiffany is in the previous three movies but does not show the Heart of Damballa, and in the original where we see Ray gunned down, the amulet is nowhere to be found.
(at around 22 mins) Tiffany locks Chucky in a playpen that rolls in and out from under a lid. However, nothing actually attaches the playpen to the lid, so when Tiffany puts a padlock onto the top of the lid to keep Chucky subdued, it technically wouldn't do anything to keep the playpen from rolling out.
(at around 1h 16 mins) The skull of Charles Lee Ray is broken off by Jade when she grabs the amulet. Later on, when Chucky is shot and falls into Ray's grave (at around 1h 22 mins), the head is fixed back on.
(at around 1h 6 mins) When David grabs Warren's gun off his corpse in the trunk and points it at Jesse and Jade, it is heard cocking. However, the gun is a Glock, which has no external hammer and thus cannot cock.
(at around 31 mins) The overhead shot of Tiffany being electrocuted in the bathtub shows water being splashed all over the floor in reverse, as if the flood the electrocution is causing is being undone.