Explosion, after which children all fall down? (7)
I believe the answer is:
atishoo
I believe this is a double definition.
'explosion' is the first definition.
(representation of the sound of a sneeze)
'after which children all fall down?' is the second definition.
(as in 'atishoo, atishoo, we all fall down')
(Other definitions for atishoo that I've seen before include "Sound of explosion" , "Word to be sneezed at" , "Sudden eruption" , "Sound of a sneeze" , "Sneezing sound" .)