Which revision correctly combines these two sentences?

It had been raining for hours. The children curled up with their favorite novels.

It had been raining for hours; The children curled up with their favorite novels.

It had been raining for hours; so the children curled up with their favorite novels.

It had been raining for hours; So, the children curled up with their favorite novels.

It had been raining for hours; the children curled up with their favorite novels.