I remember watching this movie maybe 10ish years ago about three kids who ran away from home in search of their father, who ended up being in a different realm or universe or something. I think it was two boys (the youngest could see in the future or something) and a girl. I think it was a fantasy, and suitable for children seeing as I was probably around 8. I think the opening scene was them in school.

A possibility is A Wrinkle in Time: http://en.wikipedia.org/wiki/A_Wrinkle_in_Time_(film)