B.B.
i had the same thing happen with my older daughter (she will be 5 next month) while i was pregnant with her. Both of her kidneys were slightly enlarged while i was pregnant, and they monitored her throughout the rest of the pregnancy (had me so worried). About 2 weeks after she was born she had an ultrasound that showed her kidneys were normal. All that is to say it can happen with girls too! i've actually never heard that it is more common in boys.