$n$ candies with $20 < n < 50$

If Marge divides the candies equally among $5$ children, she will have $2$ candies remaining.

so $n = 5x + 2$ so candies can be $22, 27, 32, 37, 42, 47$

If she divides the candies among 6 children, she will have 1 candy remaining.

so $n = 6y + 1$ so candies can be $25, 31, 37, 43, 49$

The common value among both is $37$

$n = 37$

If she divides among $7$ children, each will get $5$ candies with $2$ candies remaining.

Answer C