Whiteberry may be correct. It’s unclear whether our secularized American holidays bear any semblance to pagan roots.
Without getting into that issue, I’d say that if the saintly R’ Avraham Pam and others made a kiddush hashem by being kindhearted to non-Jewish children, so should we, by offering them candy.
What I’ve actually began doing in recent years is purchasing Hershey’s chocolate items after the gentile holidays (Halloween, Christmas, Valentine’s Day) when they go on sale 50=75% off and I’ve used them for shalach manos and our shul gives this candy to kids on shabbos morning (I buy whatever is OU-D, or Kof-K D, and since our shabbos kiddush luncheons are always dairy, I don’t see a problem giving a kid candy in the shape of an egg, pumpkin, or tin soldier).