The memories of childhood experiences, whether a tear-jerking boo-boo or a funky dance that sent Mom and Dad into fits of laughter, have all but vanished by the time we reach adulthood. It turns out those memories are even more fleeting than previously believed, fading between the ages of 4 and 7, new research finds.

Until now, based on studies of adults, scientists had thought that children under age 3 or 4 didn't have the cognitive or language skills to form memories. And so these memories weren't exactly lost, but were never even stored in our brains in the first place. [Read: Fetuses Have Memories]

But Carole Peterson, a psychology professor at Memorial University of Newfoundland in Canada, and her colleagues had found that young children have lots of memories they could talk about. "So it was very clear that the explanation that had been given for adults just had to be wrong, because children do have the cognitive, linguistic and memory skills to talk about things that had occurred in their past," Peterson said.

Fleeting childhood

To figure out how childhood memories fade, Peterson's team followed 140 kids ages 4 to 13, asking them at the study start and two years later to describe their three earliest memories. Parents confirmed the experiences had happened and the timing of the experiences.

Kids ages 4 to 7 at the study's start tended to recall different memories at the first interview compared with two years later, suggesting these very early memories are fragile and can easily fade away. However, a third of the children ages 10 to 13 described the same earliest memories at both time points. [Top 10 Mysteries of the Mind]

"The whole phenomenon of infantile amnesia is clearly a moving target in children, because as children move from 4 to 10, their [earliest] memories get later and later," Peterson said. "But by age 10, those memories seem to get crystallized."

In addition, for kids who didn't describe one of the previously mentioned memories at the two-year mark, the researchers described the kid's own summary of that memory. For the older kids, that was enough to jog their memory and they immediately recalled the event. But in the 4- to 7-year-old age group, the children said that had never happened in their lives. (To ensure accuracy, kids were also given summaries of three fake memories, and all kids said they hadn't experienced these either.)

Kiddy memories

As for what kids remembered, Peterson was surprised the traumatic or otherwise emotionally charged events didn't turn up very often. "One child remembered playing peek-a-boo with her grandfather around her mother's pregnant round belly," Peterson told LiveScience. Another remembered waiting for a bus with her mom and there was a flower growing up through a crack in the sidewalk.

Other memories included: a child who couldn't find her favorite bathing suit and so ripped apart her drawers to locate it; a child who would hide the new puppy the family had gotten so others had to look for it; and a child swallowing a small yellow Lego while in the backseat of the car and feeling like he was going to die, but being too scared to tell his parents.

Peterson hopes to figure out what makes some memories stick and others vanish, with this study suggesting neither the content nor the emotion attached to the memory play major roles.

The study, detailed in the current issue of the journal Child Development, suggests that our "psychological childhood" begins much later than our actual childhood.

"As we lose those memories of those early years, years that we previously could recall, we're losing part of our childhood — in essence, we're losing all or almost all of those events that occurred to us then," Peterson said.

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