4
Detail
Since the children were born at the interval of three years, let us assume their ages as x, x+3,x+6,x+9, and x+12.
given- the sum of five children is 50
therefore,
x+x+3+x+6+x+9+x+12 = 50
5x+30 = 50
5x = 50-30
5x=20
x=4
Hence, the age of the youngest child is 4 years.