"The children are walking behind their parents."
Translation:Die Kinder gehen hinter ihren Eltern.
Shouldn't "their parents" be in the accusative case since "the children" are moving?
For Akkusativ, there needs to be movement from one place to another. However, a place can be a mental area in which you can move around. You could image that the children are in a box-like area "hinter" (behind) their parents. While they keep walking behind their parents, they stay in that imaginary box which is why you use Dativ here.
So how come "die Maus läuft ums Glas" uses the accusative case, even though the mouse remains at the same area, or in the same imaginary box that wraps the glass?
The mouse isn't static in that box. The children, relative to the parents, aren't moving.