Among the heartbreaking facts that Janette Fennell keeps track of are the names of children who have baked to death in cars. This year, so far, there have been 20 child hyperthermia deaths nationwide — three of them just in the past week — and that's not counting the cases where a passer-by broke into a car to rescue a child.

Fennell's Kansas-based group, Kids And Cars, keeps track of those near misses, too, so she knows about the Salt Lake man who was charged with child abuse last week after going to see a late-night showing of the new Batman movie, leaving his 2-year-old son unattended in the car. The little boy, reportedly sweating, thirsty and crying, was noticed by another moviegoer, who alerted police.

That incident comes on the heels of two Utah hyperthermia deaths, one in April, one in June, both cases where mothers forgot their children were in the car. Parents who forget are different from those who choose to leave a child unattended, Fennell says, although the result is often the same.

If she had to categorize the latter group, she says, "it's parents who put their own convenience over the safety of child. ... It's really people tempting fate." The other group is more complicated. "It's not that they forget they have a kid," she explains. "It has more to do with how our memory works, or in this case, how our memory doesn't work." And, ironically, forgetting also has to do with the improvement in car safety.

"One of the biggest things we see," Fennell explains, "is that if we look at the number of hyperthermia deaths before 1995, they happened only once in a great while." In 1995, with the widespread use of passenger-side air bags and the resulting crusade to put children in the back seat to prevent air-bag injuries, hyperthermia deaths began to rise. The "deadly consequence," she says, is that "children are out of sight, out of mind." Add to that another safety improvement — infant seats that face backward.

Forgetting also can be blamed on the prefrontal cortex, that part of the brain that helps us multi-task but is sensitive to stress.

Yale University psychology professor Jeremy Gray offers this list of common culprits that can impair prefrontal cortex functioning: sleep deprivation, stress from work, marital problems, heat, alcohol or drugs and certain medications that impair judgment. Add to that "doing something outside your usual routine or being distracted."