Four children has 16 combinations (2^4)

Male:0 Female:1
0000
0001
0010
0011*
0100
0101*
0110*
0111
1000
1001*
1010*
1011
1100*
1101
1110
1111

There are only 6 cases with 2 male and 2 female. Result 6/16=3/8.