A child restraint device is required for infants up to 24 months. See NCO.IDE.A.140 in Part-NCO. A supplementary loop belt is typically used for an infant when placed on the lap but these aren't safe:
A 2004 Australian study [
link] found that, although the infant anthropomorphic dummy attached with a supplementary loop belt was restrained during dynamic testing, it underwent significant forward excursion resulting in severe impact of the infant dummy's head with the forward seat back. In addition, the adult dummy folded over the infant dummy trapping and crushing it in the process.
This is from appendix F to TSBC report A12Q0216 (
link). The entire appendix has been reproduced in SKYbrary article
Cabin Safety—Child Restraint Systems (
link), but see the original report for footnotes.
See also footnote 130 on a comprehensive review on child restraint systems done for EASA,
Study on Child Restraint Systems, contract number EASA.2007.C.28, published Nov 2008. That review is available from SKYbrary (pdf
link) and EASA (pdf
link). See page 27 para 2.2.4 on a C172 accident in which the sole survivor, a 3 year old child, had been seated in a child restraint system. She probably survived because supplementary loop belts aren't allow in Canada where the accident occurred.
Examples of acceptable means of compliance with Canadian requirements are given in TCCA Advisory Circular (AC) No. 605-003 (Child Restraint Systems and Other Seating Devices) (
link).