How do you mean? The Romans killed their children. The Vikings killed their children. The Anglo-Saxons killed their children. The Biblical Hebrews killed their children. The Merovingians killed their children. The Carolingians killed their children. The medieval English, German, Dutch, Swedish, Spanish, Italian and Portuguese peoples killed their children. The Aztecs killed their children.
Do you want me literally to go through every civilization picking out the ones that didn't?
Seriously, it is A Thing. It's not at all unusual.
Even if you think about relatively 'close to home' scenarios, you will find infanticide considered socially acceptable. I have mentioned abortion; if that makes you squeamish (and it does me, too), then think about babies with serious disabilities being quietly left to die in hospitals in England in the 50s and 60s, or parents being encouraged not to offer treatment to babies with conditions such as Down's, in the expectation those babies should die.
I'm sorry, it's a horrible subject, but I don't think you can insist that 'infanticide' is something rare and horrible, just because our society has drawn the diving line between 'acceptable infanticide' and 'unacceptable infanticide' differently from some other societies. Yes, we no longer sacrifice our two-year-olds in wells. But we do make determinations about what kinds of foetal and infant life will, and will not, continue.
(I think I need to stress I am not remotely pro-life and I don't have an agenda here.)