When I hear about stories of children being murdered or any gruesome horrific act such as the one you were referring to, I never even notice if it was a boy or girl. Just that it was a human being or that it was a child who missed out on their life and the experience of having loving parents to nurture them.
I don't deny the fact that there is definitely prejudice against women many places in the world but I don't think that every time a woman or girl is killed, it's because they were female. I think that you may feel that way when you read these stories because you feel so strongly about the oppression/inequality of women and thereby perhaps insinuate your beliefs onto the case, whatever it may be.
It doesn't mean that this sort of thing never happens; only that more evidence would be needed to support that theory.
EDIT: Here is a link to the US Bureau of Justice with child homicide statisics. This is only the US' statistics so not sure what other country's statistics would be...
Child Homicide Statistics
