Step 1: Finding the critical points.
Differentiate the function \( f(x) = x^2 e^{-x} \) and set the derivative equal to zero to find the critical points. After solving, evaluate the maximum value at the critical point.
Step 2: Conclusion.
Thus, the maximum value of \( f(x) \) is \( \frac{2}{e} \). Hence, the correct answer is option (C).
Final Answer:
\[
\boxed{\text{(C) } \frac{2}{e}}
\]