Let the age of the youngest child be \( x \). Then the ages of the other children will be \( x + 3 \), \( x + 6 \), \( x + 9 \), and \( x + 12 \), as they are born at intervals of 3 years.
The sum of their ages is:
\[
x + (x + 3) + (x + 6) + (x + 9) + (x + 12) = 50
\]
Simplifying the equation:
\[
5x + 30 = 50
\]
\[
5x = 50 - 30
\]
\[
5x = 20
\]
\[
x = 4
\]
Thus, the age of the youngest child is 4 years.