i-Size is an EU safety regulation for child car seats and is intended to make car seats easier to use and safer for children in the event of a collision. This standard is only used for ISOFIX seats. i-Size seats are categorized based on height and not age. The Bugaboo Owl by Nuna can be used from birth (minimum 40 cm/15.75 in). With the adjustable headrest, it can be used until your child has reached 18 kg/40 lbs and 105 cm/41.3 in.