Cybex Aton M i-Size The Aton M i-Size offers the latest safety technology available. When installed with the Base M (additionally available), the infant car seat complies with the i-Size regulation. i-Size (UN R129) is the EU standard for child safety, making rear-facing travel mandatory until your child reaches 15 months. The Aton M i-Size can be used for newborns and babies from 45 cm in height up to 87 cm and max. 13 kg.