See also:

Unfastening the seat belts
1 To unfasten the seat belt, press the button on the buckle. The seat belt automatically retracts. ...

Larger children
Children who are too large for child restraints should be seated and restrained by the seat belts which are provided. The seat belt may not fit properly if the child is less than 4 ft 9 in (142. ...

Boxy Dynamics
I have no reason to believe the Cube is unstable, and it has a standard electronic stability system, but it does feel more top-heavy than the other boxes — and definitely more so than convention ...