Answer
$0.25$
Work Step by Step
We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$. We have
4 children, each of them can be a boy or a girl, therefore the number of opportunities is $2^{4}=16$, from which 4 are good because the following 4 opportunities are good: BGGG, GBGG, GGBG, GGGB. Therefore $probability=\frac{4}{16}=0.25$.
