Answer
The required probability is, $\frac{1}{2}$
Work Step by Step
We know that the sample space of equally likely outcomes is $\left\{ MMM,MMF,MFM,MFF,FMM,FMF,FFM,FFF \right\}$
Thus $ n\left( S \right)=8$
Assume $ E $ to be the event of obtaining at least two female children; then, we get $ E=\left\{ MFF,FMF,FFM,FFF \right\}$
Therefore, $ n\left( E \right)=4$
So the probability of getting at least two female children is:
$\begin{align}
& P\left( E \right)=\frac{n\left( E \right)}{n\left( S \right)} \\
& =\frac{4}{8} \\
& =\frac{1}{2}
\end{align}$
