The only reasons for a sandpit to be disinfected is if cats have urinated or defecated in the sand, or if the sand is extremely dirty (for example, if it has a very high level of use) as basic bacteria will not survive in a sandpit as the tonicity would be too high for them and the cell membrane would rupture (i.e. water would be drawn out of the bacteria’s cells into the drier environment surrounding them).
The recommended procedure for cleaning a sandpit is to clean the sand with a sterlising fluid spray or liquid sterilising solution of a suitable concentration. Spray or pour the solution over the sand using a plastic watering can. Turn over the sand after 15 minutes and repeat until the area has been covered. Ensure the sand is reasonably dry before children continue to play in it.
For more information, see www.rospa.com/play-safety/Advice/Sand-Play