Jurassic Park
In Jurassic Park, little Tim is climbing an electric fence when suddenly sparks fly out from the wires, causing him to fall backward. However, it is obvious that the sparks are nowhere near Tim's hands, and even if they had been, the boy would have likely been killed by the voltage.
American Sniper
In a since-deleted tweet, American Sniper screenwriter Jason Hall explained the reason for the fake baby at the end of the film. Claiming that he hated to "ruin the fun," Hall said that "real baby #1 showed up with a fever" and "real baby #2 was no show." Thus, fake baby. Although, to be honest, at that point, it might have made more sense to write the baby out of the scene.