0.3125.

Step-by-step explanation:

- The chance of having a boy is 0.5,

- the chance of having a girl is also 0.5.

Outcome 1: all boys

boy boy boy boy

0.5 * 0.5 * 0.5 * 0.5 = 0.0625

Outcome 2: first child is a girl, all others are boys

girl boy boy boy

0.5 * 0.5 * 0.5 * 0.5 = 0.0625

Outcome 3: second child is a girl, all others are boys

boy girl boy boy

0.5 * 0.5 * 0.5 * 0.5 = 0.0625

Outcome 4: third child is a girl, all others are boys

boy boy girl boy

0.5 * 0.5 * 0.5 * 0.5 = 0.0625

Outcome 5: fourth child is a girl, all others are boys

boy boy boy girl

0.5 * 0.5 * 0.5 * 0.5 = 0.0625

Therefore,

0.0625 + 0.0625 + 0.0625 + 0.0625 + 0.0625 = 0.0625 * 5 = 0.3125