While there has been a few error with the timeline between Rise of the Guardians and the Guardians of Childhood series, we can conclude that they have the same continuity and not a different universe or timeline.
The creator, William Joyce, has said that the movie takes place a 200 years after the books and there's also hints in the movie that help with this facts.
In The Sandman and the War of Dreams, a lot of new connections have been made to the movie.
In the books, North was thief but after been chosen he becomes an inventor that sees wonder in every little thing. In fourth chapter book, it's reveal that North has become "jolly" (or like of the Williams said FAT!) for eating to many Yetis' cookies.
He also used the sleigh to go anywhere.
Bunnymund is one of the character that changes the most from books to movie. When he first appear, he was dress in robes (more like a sage).
In the movie there's a hint of this at the Tooth's Palace, after Pitch left and Tooth explained to Jack about being chosen she said:
"We were all someone before we were chosen…"
With North then said: "You should have seen Bunny!" and Bunny responded: "I told you never to mention that."
This implies that somewhere in those 200 years Bunnymund changed his outfit to the one in Rise of the Guardians. Also is you see the small pictures draw in the pages of the books we can see the transformation of Bunnymund. By the end of the fourth book, Bunnymund looks more like the RotG Bunnymund with only pants covering his lower half.
Also when Bunnymund first appear, he talks in "big words" making him sound like a know it all but by the fourth chapter he has become less uptight.
When Toothiana first appeared, she collecting teeth and in one of this journey she meets the Guardians but at the end of the fourth chapter book she has created 1000 and 1000 of fairies to help with construction of the North Pole.
So what does this have to do with the movie? If she created so many fairies, that means she can send them around the word to collect the teeth while she can just tell them where to go.
In the movie, she said that she hasnt been on the field by 400 somethings years but this an error since the books happened 200 years before but it amazing how they are trying to connect the movie with the books.
In the third chapter book, there was a hint that Jack would appear in The Sandman and the War of Dreams but he wasnt in the final cut.
The reasons for this is because Jack shouldn't be a Guardian until the movie.
In the fourth chapter book, the guardians created the North's Workshop so it wont make sense for Jack to be there since he said that he has been trying to break in for years.
Another reason is the Man in the Moon, in the movie he has taken a sit back while in the books he is heavily involve with the Guardians. Jack been there will caused confusion since in the movie he have asked MiM for his purpose but MiM doesn't respond.
I won't be surprise if by the final chapter the creator give us a hint saying about a boy and a girl skating in tin ice while the man in the moon watches from above.
Another hint is when Pitch confronted Jack in Antartica, Pitch mentioned looking for a family. This is a reference to Pitch looking for his daughter, Mother Nature, in the books.
In the fourth chapter books, Katherine has a dream about a cow, 3 mice with black glasses and dish and a spoon. This are hints that states Katherine is Mother Goose.
- 3 mice wearing dark lensed glasses - 3 blind mice
- A leaping cow - A cow jumps over the moon
- a dish and a spoon
While Mother Nature, Katherine, Nightlight and Ombric don't appear in the movie, it's implied that they still exist in the timeline as the North Pole is a result of Katherine's dreams in the books.
I'll be trying to find a few more hints but if you find a new one just add it or comment below. I love figuring out stuff.