Kicks...like any other attack occur in either a vertical or horizontal plane. Aikido is well versed to handle kicks via the standard applications...i.e. irimi and tenkan.
Irimi works well for those attacks that occur in the Vertical plane..tenkan works well (sometimes coupled with irimi) in the horizontal.
The problem lies not in the application of technique but mindset. The first inclination is to block...but as my wise old Sensei told me..."If you have time to block, you have time to move" it's just a different set of muscles. Blocking is a situational response to a attack, Movement (irimi and tenkan) is a strategic response....moving to a place of specific advantage in relation to an attack. You change the line of attack to your advantage..it's a different mindset than the common aikido adage "get off the line". More realistically it is " Get off the line at the point where you have the upper hand."