"Understanding distinctions between types of child abductors and abductions is important in investigating and solving the cases," he said.
"It may, however, have little, if any, legal significance and should not automatically imply that one is a lesser crime or one offender is less dangerous or culpable."
James Fox, a criminologist at Northeastern University in Boston, agreed with the distinctions.
"Infants are stolen to take possession or also for ransom," he said. "Older children either for sex or also for ransom.
"You see, older children cannot easily be convinced of different parenthood, while infants are not especially appealing to pedophiles."
The age of the child is important in determining how to profile the kidnapper. The missing children's center defines an infant as a child younger than 1.
Although a teenage victim is technically a child, she has more in common physically with a 20-year-old, who is an adult, Lanning said. Prepubescent children -- ages 12 and older -- are more likely to be the victims of a sexual crime.
"Ted Bundy's last victim was a 12-year-old girl, but most people don't think of him as a pedophile," Lanning said. "Technically, she was a girl, but the physical characteristics of a 16-year-old, for example, are more like a 26-year-old."
In the Jaycee Dugard case, for example, Phillip Garrido may have eluded the law for so long because police had discounted him as a sex offender, because they were erroneously looking for a pedophile.
"This guy had a botched abduction of an adult and so he goes for something younger who is easier to control and uses a woman to help him," Lanning said. "He interacts with her for the next 18 years as an adult woman and she becomes the mother of his children."
Unless the kidnapper has a rare and odd proclivity, those who abduct the youngest children are almost always women and usually those from low socio-economic backgrounds who have a dependency on their male partners, according to FBI studies.
"A very high percentage of women who abduct infants, not necessarily all of them, do it to have a baby," Lanning said. "And that doesn't mean every time an infant is abducted we know that 100 percent. A tiny percentage is sexually aroused by babies."
In a case in California, two men kidnapped a baby to raise her as a "breeder" to bear children so that they could later molest them, Lanning said. "You are dealing with an isolated situation. … We know the more common reason people abduct adult children is money, ransom, sex and murder."
Infant abductors can be "very clever," Lanning said.
One woman, whose husband was in jail, abducted a 4-year-old child, ruling out an infant. She reasoned that he would not have been fooled if she had given birth to an infant, because "he wasn't around" to have sex with her and be the biological father.
"She wanted to preserve her relations with her man," Lanning said. "She didn't need a baby; she needed a husband or a boyfriend and convince him it was his baby. It had to be 4.
"The key thing is that doesn't get reported is these women don't adopt or take in foster children because they have to go home and say to the boyfriend or husband, 'Here is your baby,' and that's why many of them fake pregnancies."
Women plan these crimes for months and are "creative and clever and cunning," he said.