I never heard of it until now.
A UN resolution (66/170) created this back in 2011; the full name is “International Day of the Girl Child” in fact.
UN resolutions are typically communistic, and promoting of hatred, e.g. Resolution 3379.
‘k, now it all makes sense.
There is also an International Men’s Day and an International Day of the Boy Child, but neither the UN nor the US government has officially recognized them. There is a National Sons’ Day — there’s a National everything day, it seems — but I don’t know if the government officially proclaimed that either.