Is it permissible for the younger, pre-pubescent sister to sleep between her two adult sisters in one bed?

The Sunnah indicates the obligation to separate children in their sleeping places when they reach ten years of age. This separation includes males and females together, or males alone, or females alone. This separation is explained in two ways: either each of them has their own bed, or they sleep in one bed but separated and not touching each other. It is preferable for each of them to have an independent bed. If that is not possible, there is no harm in them sleeping in one bed, provided that each has her own cover.