The range of "normal" chicken poo is quite wide. The white from their droppings is from the uric acid and is normal. The loose consistency can be due to a number of factors such as worms. However, in the summer time, the most common cause is heat. The birds will use loose droppings as a way to expel excess heat. I would keep an eye on them and if their appetite and appearance is normal and you don't see any worms in their droppings, then they'll be fine. I wouldn't be alarmed unless this persisted for a number of days or a week.