FORD 2013 Flex v.2 - Manual (Page 22)

If the booster seat slides on the vehicle seat, placing a rubberized mesh
sold as shelf or carpet liner under the booster seat may improve this
condition. Do not introduce any item thicker than this under the booster
seat. Check with the booster seat manufacturer’s instructions.
INSTALLING CHILD SEATS
Using lap and shoulder belts
WARNING: Airbags can kill or injure a child in a child seat.
NEVER place a rear-facing child seat in front of an active airbag.
If you must use a forward-facing child seat in the front seat, move the
seat all the way back.
WARNING: Children 12 and under should be properly restrained
in the rear seat whenever possible.
22 Child Safety
2013 Flex (471)
Owners Guide gf, 2nd Printing
USA (fus)