Mercedes-Benz GLB Owner's Manual page 66

Weight group 0+ (up to 13 kg and up to approx. 15 months) for third row of seats
Size class:
E
D
C
Weight group 1 (9–18 kg and approx. 9 months to 4 years)
Size class:
D
C
B
B1
Equipment: Left/right rear seat
ISO/R1 IL
ISO/R2, ISO/R2X X
ISO/R3 X
IL Suitable for ISOFIX child restraint systems according to the table in "Overview of the recommended child restraint systems", or if the
vehicle and the seat are listed on the child restraint system manufacturer's vehicle model list.
X Not suitable for an ISOFIX child restraint system in this weight group and/or size class.
Equipment: Left/right rear seat (second row of seats)
ISO/R2, ISO/R2X IL
ISO/R3 IL (1)
ISO/F2 IUF
ISO/F2X IUF
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Occupant safety