I've noticed in both the manga and the anime, the tailed beasts tend to appear in different sizes. Sometimes they are extreamly large and sometimes they are not that large. For example, Kurama seemed very large when he attacked Konoha but in other occasions, he seemed pretty smaller. Not only Kurama but also other tailed beasts like Shukaku. Can the tailed beasts change their sizes or was this just an error done by the animators?
I think it's one of the little details changed from the Original. Instead of being immensely Titanic in size, they are smaller in Shippuden, enough small for a shinobi to have any chance. The Tailed Beasts and the Summons(They had their size change too) got smaller than usual. This is the reason, I think.
Can the tailed beasts change their sizes or was this just an error done by the animators?
Most often, directors and such have specific images in mind when making scenes. That means that often scales are intentionally warped to get a certain effect or shot. So it's not so much an error as much as it's intentional.