Yeah, I was going to suggest W&G Were-Rabbit as well. The eight year old tolerates it well enough.
I seem to be tougher when it comes to horror flicks (not slashers though).
I saw it when I was six, but the eight year old can't handle it is, Gremlins. I think that takes place on Christmas though?
Little Monsters is good, but not very Halloweeny.
Nightmare before Christmas is high on my list, I'm just never sure when I should show it.
E.T. was already recommended, but I'll include it here.
Not really Halloween films, but I've always had a fondness for
Night of the Comet
House
Maximum Overdrive
all of which I've seen before the third grade.