I have a copy of Lego Star Wars: The Complete Saga (Nintendo DS). I got stuck on episode 1, chapter 4, specifically on the puzzle with the hatches and the boxes. I switch to little Anakin to crawl through the hatch, and when I exit the other hatch, I switch to Qui-Gon to smash the block. I can't seem to figure out how to switch back to Anakin. (I'm sure the solution is very simple, but I don't have the manual!)
I ran into this issue as well. You can actually clear the gap by double jumping with Qui-Gon or Obi Wan. Even if you can't make it all the way across, you might be able to switch characters while in the air.
I managed to do this on the iOS version of TCS, but this tactic should also work in the DS version.