The most terrifying part was not the dated period clothing, the soulless eyes of the dolls, or even the fact that some residents noticed a passing resemblance between the dolls and their daughters. It was the total randomness of the dolls' placements, spanning multiple neighborhoods over the course of a week. There were no notes and no clues -- only a vague feeling that something terrifying was about to happen.
Orange County Sheriff's Department
"We've narrowed it down to 'Restless 19th-century ghost' or 'Threat from eccentric mafia don.'"
Upon realizing that they were trapped in the beginning of a Bride Of Chucky / X-Files crossover, residents began to call the police. After some top-notch detective work, the police announced that their search had led them to the culprit: a sweet innocent old woman who went to church with many of the recipients. Wes Craven himself could not have scripted a creepier setup.
Fortunately, the dolls were not an omen of death so much as they were an omen of Old Lady Trying to Interact With Her Neighbors. The police found that the dolls were being dropped off "out of goodwill and that [the woman] intended it as a kind gesture," and it seems she hadn't seen enough horror films to realize the terrifying nature of magically-appearing porcelain dolls. Hopefully, she sticks to baked goods the next time she wants to do something nice for the neighborhood.