It's easy to pick on the Spartiate, but the fabled Athenians engaged in it also.
http://ancienthistory.about.com/library/bl/bl_text_wsd_sec27.htm
Thanks for the link
ALL classical peoples practiced infanticide, with the sole exception of the Jews.
It was routinely cited by Greek/Roman writers as an example of how weird the Jews were. Why, they raise all their children, even the girls!
In almost all cultures, the decision whether the baby would live or die was left up to the male head of household. AFAIK, only the Spartans involved the state directly in these decisions.
BTW, these children were usually exposed, not killed directly. Childless couples would go “shopping” in the known exposure areas, and many would pick up a likely child and raise him as their own son. In certain times and places there was a cottage industry of people who would rescue these babies, raise them to a salable age and sell them on the slave market. So by no means did these children always die.