What's the best disinfectant?

Hi I let my girls free-range round the garden.  It is mainly slabbed and I poo pick every day.  Usually I or hubby just throw a few buckets of water over the slabs or hose it and brush it. For future reference when the weather gets better and my grand-daughters come round and want to play in the garden, whats the best disinfectant to use? Dont want to poison my girls (the chickens that is  )
Jinty
 

with having a run on slabs i have been told to put straw down as the girls feet dont like it, but then what i know at the moyou can put on the back of a postage stamp