The following is some information drawn from a report conducted for the German CAA that outlines what flyblue was speaking of...
JAR-OPS 1.320 and 1.730 outline, among other things, the transportation of infants and children. The provisions allow multiple occupancy of aircraft passenger seats. Accordingly, infants (< 2 years) are properly transported on an adult's lap. JAR OPS 1.730 further regulates that an operator is only allowed to operate an aircraft if he or she provides an additional loop belt or other restraint device for each infant.
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For the transportation of infants on an adult's lap, the adult is restrained with a pelvic belt, and the infant is fixed on the adult's lap with an additional loop belt.
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In a suddenly occurring deceleration in the longitudinal aircraft axis, the adult and the infant show a pronounced jack-knife effect. The upper torso and the lower extremities of the infant as well as of the adult sitting behind the infant fold up in a forward direction, with the loop belt restraining the infant. Finally, the loop belt drives into the infant's abdomen and only stops at his or her vertebral spine. From the technical point of view, the infant acts like an energy absorption element for the adult; the crash loads acting on the adult are thus reduced, and the infant fixed with the loop belt thus suffers most serious up to fatal injuries.
Examination on the Enhancement of Cabin Safety for Infants