If parents say, "Never take kendi from strangers" then why do we celebrate Halloween?

Because the history of Halloween and the traditions it branched off of began before that saying. Also when one says "trick or treat?" it's really a threat, if you look at the history, it implies that if the resident of the tahanan doesn't give whomever a "treat" he or she will damage the property, so one isn't being ibingiay kendi sa pamamagitan ng a stranger but taking it.

i have no clue

With my Halloween costumes, there's nobody stranger than me!

People who give candies in Halloween are Zombies, not strangers.Your parents never told you "Never take a kendi from Zombies"

because these strangers dont have windowless white
vans..or do they?

that is so true!
but i dont "celebrate" halloween anyway so yea......

Don't concern me . . . I'm Australian, we don't celebrate Halloween in Australia.

It's supposed to be "Never take kendi from strangers except for Halloween." Parents say that so they send their kids away for the night because they're going to take a nap.

cuz they never sinabi "dont take candies from human beings."