The Grants ad above is interesting in that the only licensed character costume is Yogi Bear – a favorite of mine. The "smarter than the average bear" was introduced on The Huckleberry Hound Show in 1958, and had received his own TV show in 1961.
I supposed his visibility had received another boost in 1964, thanks to the release of his full-length movie Hey There It's Yogi Bear earlier that year.
I like that little witch icon done in the style of a child's doodle in the Grants ad. Apparently it was used on the Mars candy bar packaging that year, since it seems to be visible in the candy illustrations as well.
But what about the other costumes in the ad?
As for the generic Frankenstein monster outfit, I couldn't quite find an exact match. But here's a link to a great blog featuring a variety of vintage Ben Cooper monster costumes that probably includes the one shown.
And for a hilarious look at kid's Halloween costumes of the 1950s and 60s, click here to visit John Kricfalusi's blog.