Let the age of the mother be G.
i)
"Kid A is half the mother's current age."
thus, the age of Kid A is G/2
ii)
"Kid B is 4 years younger than Kid A."
this means, the age of Kid B is the age of Kid A - 4 = G/2 - 4
iii)
"In 3 years, Kid C will be 1/5 of his mother's age (not her current age). "
thus, in 3 years the age of Kid C will be 1/5(G+3)=1/5G+3/5
this means that the current age of Kid C is
1/5G+3/5-3=1/5G+3/5-15/5=1/5G-12/5 = (G-12)/5
The ages of the Kids A, B and C are:
G/2 , G/2 - 4, (G-12)/5
From the smallest Child's age (G-12)/5 we understand that G-12 is a multiple of 5,
so G-12 ∈{5, 10, 15, 20, 25, ....}
which means G∈{17, 22, 27, 32, 37, 42, 47, 51, 56, 61... }
From the age of the oldest child G/2, we understand that G must be an even number (so that G/2 is a whole number).
This means that G∈{22, 32, 42, 56,...}
If G was 22, the oldest child would be 11, which makes no sense
If G is 32, the oldest child is 16, which means the woman became a mother at the age of 16, which is rare, but possible.
then G/2=16 , G/2 - 4=12, (G-12)/5=(32-12)/5=20/5=4
If G is 42, her oldest child is 21, no more a "kid", but still, lets consider this case:
the age of the second child is 21-4=17, and the youngest (42-12)/5=6
Answer:
The Plausible cases are :
i) mother: 32, children 16, 12, 4
ii) mother: 42, children : 21, 17, 6