The sample space for the number of boys, and number of girls in a family with exactly three children is
S = {GGG, GGB, GBG, GBB, BGG, BGB, BBG, BBB}
These are
GGG/BBB = three girls / three boys with a probability of 1/8.
GGB, GBG, BGG = two girls, and one boy, with a probability of 3/8
GBB, BGB, BBG = two boys, and one girl with a probability of 3/8
Summarizing, the outcomes are
{3 boys, 2 boys and 1 girl, 1 boy and 2 girls, 3 girls}; The outcomes are not equally likely.