but you could make a variable and in SceneUpdate for example pause=0 at start of the game, pause=1 when pause.
and just wrap "if"-statement the game logic (player move etc).
So when player goes to menu, other things goes to pause (i think this atleast work with LUA, and in C++ , well might take few more lines of codes because you write ai in c++? maybe add behaviour that just dont do anything or something)
also if you have object you have to getCentralForces ( i think, im noob in coding with LUA still...) and somehow save them and stop all forces (clearForces)
Correct me if im wrong tho 
but basically i think that you have to save current scenes forces, behaviours etc, clear them (stop them moving) when going menu,
and when coming back put all forces back... but this will be problem when multiple objects... (first objects have their forces and the other dont yet (end of the list))
