I too agree that a seat for every pax is the safest way but unfortunately, I can't see it happening anytime soon. In the meantime, how is a baby "tied" to your lap potentially serious? Surely, it's got to be better than a completely unrestrained infant? I'm not trying to be argumentative as you may well be thinking of something that hasn't even crossed my mind, hence the question.
While a number of aviation authorities still require the use of the loop belt, others have chosen to no longer permit it's use due to testing and research related to the hazard it poses in an accident scenario. One example of such a report is from Germany:
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
For children ages 1-4, there is the
AmSafe CARES device that is now available for use. Quite a few authorities have indicated that they will accept its use on board, including the
UK CAA.