When the kids were younger and we had au pairs living with us, we made an effort to share American culture with our au pairs.
There are a number of holidays that both Americans and Europeans observe - Christmas, Easter, independence days, New Year's, etc. Yes we had different cultural spins but these holidays were familiar to our au pairs.
Halloween has no European cultural equivalent. The pumpkins, the costumes and the candy are uniquely ours.
Even though we are far from home, we are not far from Halloween. The commissary sells pumpkins and Halloween candy. The PX has Halloween costumes and decorations. Club Beyond (the youth ministry here) had a pumpkin carving evening. Americans are kind of spread out throughout the Mons region, so trick or treating is not quite possible - but the kids can dress up and enjoy trunk or treat.
Here and there I've noticed shades of Halloween among the Belgians. There are some Halloween type decorations for sale in the local supermarket and I've seen some small nods to it in the neighborhood. I'm not talking about lovely fall decor - pumpkins, hay and mums. I'm talking jack-o-lantern pre-printed/factory made stuff.
If one must adopt American stuff, I think, they should take the best part. Factory made decor not being what I consider the best part.
The best part is trick or treating - costumes and chocolate. And here that would be costumes and Belgian chocolate.....