I swear I remember seeing this movie when I was a kid in the early 80's. The only thing I can remember is that it started as live action and I think it was a boy that somehow went into this box and then it turned into animation. There could have been a girl too. Sorry for not many details!

You could be thinking of The Phantom Tollbooth.

Thank you for answering-I am positive that is the movie! As soon as I saw the name it came back to me! I know I saw it in a theater when I was a kid.

Okay I just looked it up and the movie was made in the late 60's but I did see it in the 80's. That is it-I remember the kid finding the gift in his room then turning into animation even though I don't really remember the whole plot.
Thanks again!