If you let your kids have fun wave jumping on the beach and then leave their clothes on the sand, the clothes will get full of sand.
If you then place said clothes in a bag and bring them home to be washed, they will be wet and full of sand!
This is where the lesson is then learnt......you can not just place said clothes in the washing machine with the rest of the dark load!!
The sand will wash out of the clothes they were in and attach themselves to all the other wet washing in the machine!
When cycle has finished you will have one huge load of wet washing, covered in sand!
Moral of the story........rinse the clothes before placing them in a washing load.
Ok point taken, lesson learnt for next time!