CAA wording seems slightly woolly - use of "aim", "should" and "ideally" rather than "must". Leaves plenty of wriggle room. Presumably explains press reports of children being separated from parents on aircraft.
Raises question of who (notionally) assumes responsibility for supervising evacuation of unaccompanied children and infants - does it reside with adult sitting next to them. i.e An infant is plonked next to you and you are now "in loco parentis" ? Similarly, who is responsible for ensuring children & infants observe cabin safety announcements ? Of course, as CAA recognises, in real life, parents are going to go to the aid of their children in an emergency, even if that means battling against flow of departing pax.