it's been a while since i finished that level, so forgive my memory. as i recall, you just need to remember that the dog can jump pretty far. i remember having the heavy guy push the silver box over, but then i had him jump across to the right to push the box over later in the level. i pushed the left small box over after the silver. then, i climbed down and helped set up the boxes so the kid could hop across. i believe i maneuvered the boxes into steps that the dog could climb up, then once he was on top, i had the heavy guy drop the right box down. by then, the kid was already on the left, and i just need the dog to get up one more step, and then he could jump across.
i'm sorry i'm not clever enough to give you step-by-step. if you still can't figure it out with this hint, let me know and I'll replay the level and get you the step-by-step directions.
hope this helps.
ps: i'm assuming you know how to get the kid from the right side of the screen over into 'play', right?
Assume you know how to save boy and get Mr Esc to top level.
Get Mr Esc to push box on right hand side down. Jump over and rescue heavy man. Go down rope and push left hand box one space. Rescue dog and open door with key and let boy through. Get both to left hand side. Get heavy man to push down large block. Get dog up on block but far right. Get heavy man to push down small box and get dog to jump up and box and jump across to left hand side. Now you should be able to rescue them all.