have used similar shelves in the past (billy shelves). the L shap bracket is suprisingly good at standing the test of time.
If there is a 6.5cm distance to the wall, I would recommend cutting the relevant bit off the bottom of hte shelf. That way it goes directly against the wall and you can apply/use as many brackets as you feel are necessary.
If its not a billy shelf, but one of the designs meant for a childs room, as long as there are not extra shelves you have bought to add on top, there are very difficult to pull down by any child.
As a last point, although it sounds silly suction cups are surprisingly resilient and is flexible.