the punnett square
It's used commonly to estimate the traits of a child of two parents. For example, the probability of the child having blue eyes, or curly hair, or even having genetic disease.
There is no simple answer to the question because the children's genders are not independent events. They depend on the parents' ages and their genes.However, if you assume that children's genders are independent events then, given that the probability of a girl is approx 0.48.
The probability is 2 - 6
The probability is zero! There is no such thing as "normal". Every child (and adult) has some unique characteristics and that makes them not normal - in that respect.