Updated

Innocent faces smiling from milk boxes have served as a chilling reminder that childhood is not always safe in America.

Not all of those missing children are found, and regrettably, some of the cases end in tragedy.

Below are some of the most shocking cases of missing children — some of which changed the way law enforcement officials respond to kidnappings.

Click here to see photos of the children.

Caylee Anthony

A Florida medical examiner confirmed Friday, Dec. 19, that the tiny skeleton found outside her mother’s house was that of Caylee Anthony, dashing the hopes of the entire country that the little girl was alive. The three-year-old was reported missing in June 2008 and her mother Casey has been charged with murder.

Elizabeth Smart

For nine months, the nation held its breath waiting for news of 14-year-old Elizabeth Smart, who was abducted from her bedroom in Salt Lake City, Utah. A break in the case came when Smart’s sister recalled a man’s voice the night of the kidnapping, and an artist’s sketch of the suspect was released on “Larry King Live.” Smart and her kidnappers were found a few miles from her home, but the suspects were declared unfit to stand trial.

Madeleine McCann

The world watched for months as police and the British parents of little Madeleine McCann searched Portugal and the rest of Europe for their daughter, who vanished from their hotel room a few days before her fourth birthday. Portuguese officials and Madeleine’s parents were the subject of harsh public criticism. In the end, Madeleine remains missing.

Adam Walsh

The 6-year-old Adam Walsh disappeared without a trace from a mall in Hollywood, Florida, in July, 1981. Months later, police found his severed head in a Florida canal. In December 2008, police announced Adam’s kidnapper was Ottis Toole, a deceased serial killer who admitted to the child’s murder but later recanted. Adam’s legacy includes the television show “America’s Most Wanted,” hosted by his father, John Walsh, and the Adam Walsh Child Protection and Safety Act, which created a registry for child abusers and toughened punishment for crimes against children.

Charles Lindbergh Jr.

The nation was stunned when famed aviator Charles Lindbergh’s toddler vanished into thin air in 1932. A ransom note was left in the boy's second-floor nursery. Over 10 ransom notes followed, and the FBI launched a massive investigation. Tragically, the "Lindbergh baby" was found dead on May 12, less than three miles from the family estate. Charles’ case led to the Lindbergh Law, which made kidnapping across state lines a federal offense.

Megan Kanka

When 7-year-old Megan Kanka never came home from a bicycle ride around the block of her New Jersey neighborhood, her devoted mother brought the small-town tragedy to the hearts, minds and laws of the nation. Megan, who was kidnapped, raped and murdered by a repeated sex offender living across the street, is immortalized in Megan’s Law, which requires authorities to notify communities when a convicted child predator moves to the neighborhood.

Jessica Lunsford

Police think 9-year-old Florida girl Jessica Lunsford was buried alive in a trash can in the weeks after convicted sex offender John Couey snatched her from her bedroom in 2005. Couey was sentenced to death, and Jessica’s Law was passed, requiring restrictions like electronic tracking devices for convicted sex offenders and longer prison sentences.

Sarah Lunde

A massive search for 14-year-old Sarah Lunde gripped the country for a week in 2005 before the girl’s partially clothed body was discovered in a fish pond near the Lundes’ mobile home in Florida. David Lee Onstott, a convicted rapist, confessed to strangling the girl after getting into an argument with her mother, who once dated Onstott. Sarah’s kidnapping came on the heels of Jessica Lunsford’s.

Etan Patz

The disappearance of Etan Patz stunned New York City on May 25, 1979, at a time when missing children had little political or media attention. The 6-year-old vanished on his way to meet the school bus in Manhattan. His kidnapping prompted the milk carton campaigns, and May 25 was declared National Missing Children's Day. Etan’s body was never found.

William Ownby and Shawn Hornbeck

Shawn Hornbeck’s hellish four-year ordeal began when he was abducted while riding a bike near his home in Richwoods, Mo. In 2007, authorities searching for another missing boy, 13-year-old William “Ben” Ownby of Beaufort, Mo., found both boys in Michael Devlin's apartment in the St. Louis County town of Kirkwood. Devlin is serving three life sentences for kidnapping, sexual abuse and attempted murder. The boys were reunited with their families.

Shasta and Dylan Groene

Shasta Groene was only eight when Joseph Edward Duncan bludgeoned her older brother Slade, her mother and her mother’s boyfriend to death in their Idaho home in May, 2005. Duncan kidnapped her and Dylan, 9, her brother, taking them to western Montana to rape and torture the siblings. He killed Dylan before turning up with Shasta at a Denny’s restaurant. Duncan is serving six life sentences in prison.