Help counting

bbggg

gbbgg

ggbbg

gggbb         four ways for the two boys......but the two boys could switch places making 8 ways for the boys to be in line

                        then the other three spots can be filled by the girls   3 x 2 x 1    6 ways

 

8 x 6 = 48 ways    (this assumes the boys and girls are distiguishable)

If you want to assume that the children are not identical then you tie the boys together and not you have 4 'children'

they can be arranged in a line in 4! ways.  But either one of the boys can be to the left so we need to double this answer.

 

4!*2 = 48 ways