When Goku and Vegeta are trapped in the head of Super Buu in episode 259, you can see them travel long distances since they are so small that they have to find themselves a way trough the head of Buu (where they have to fight the evil Gotenks and Piccolo aswel). However, when Super Buu is transforming, in what will later be Kid Buu, Goku and Vegeta find the exit by traveling along with Buu's steam when he gets angry.

So what I actually want to say is: when you see them first coming out of Buu's body, they are as small as they were in the body and you can notice that with that size (compared to Buu's head), they could have never traveled that long.

They filled a whole episode with this..