Celebrations and Customs

Muslim child celebrating Halloween in school

Q: In school, the teacher and students celebrate Halloween. Can a Muslim child (7 years) celebrate Halloween with the teacher and other students? Can the Muslim kids just celebrate it for fun? Is it kufr to celebrate Halloween?

If the teacher gives some gift to the Muslim student, for example, some sticker to colour and a pumpkin mask for Halloween, can the kids play with it (the kids don't know about Halloween)?

Muslim attending non-Muslim festivals

Q: Is it allowed to accept an invitation from non-Muslims during their festivals which involves shirk (ganeshotsav) and go and eat with them?

We live in a building with all non-Muslims and they gather at night and perform rituals of festivals, sing songs and listen to songs with music on loudspeakers. One non-Muslim has invited all people of building for food.

Unintentionally purchasing a heart shaped doughnut on Valentine's day

Q: I bought a donut from Dunkin Donuts because I was hungry and it ended up being heart shaped because of Valentine’s Day. I do not celebrate Valentine days and did not know that it would be heart shaped. I was not sure if I should return the doughnut but did not want to waste food so I ate it. Did I commit kufr or a sin ?