I saw it when I was a kid. I think it had siblings that were bored and then slid down the slide and the world was transformed into this exciting cartoon world. It was over ten years ago, so I may be wrong with the details... And there was a tiger that was mean, but secretly was sad. I remember him singing the song while hiding behind a tree?

Wee Sing in the Big Rock Candy Mountains (http://www.imdb.com/title/tt0386866/)

THANK YOU SO MUCH!! That's IT!! I thought I was crazy!!

You're very welcome.