What 1960's film involved kids traveling back to prehistoric times?

[sacesta]

Hi,  I'm new to this forum and I have a question for you.

I remember seeing at the theatre, as a kid in the late sixties, a film about a group of kids that somehow traveled back to prehistoric times.  The memory is very vague, but I recall that these kids traveled by raft on a river and if i remember correctly the further they traveled the further back in time they went.  It made quite an impression on me back then and my vague memory of it has been haunting me for a very long time.  

Does anyone have any information about that film?

Steve

[JJ80]

Possibly this:

http://www.imdb.com/title/tt0047930/

[Jordan]

That's the movie that came to mind when I read the description too.