Student or Learner
Don't horse around at the top of the stairs. Either come down here or get back up there (I shouldn't be able to say that because he's already at the top-most step, which would already be the next floor).
Would by the stairs be more appropriate? I didn't use by the stairs because I thought it could also mean by the foot of the stairs (what I meant by that is at the ground near the bottom of the stairs), and I want to emphasize the fact that he shouldn't horse around at the top of the stairs because he might fall.
Would Either come down here or get farther away from the stairs be more appropriate?
Not a teacher.
Move away from the top of the stairs.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.