I found the description of where to go in the Walkthrough to be slightly confusing, so adding this solution as a bit of an extra. The text below is copied from the Walkthrough with a couple changes because there is a quicker way and an easier explanation.World 7-3
As the level starts, you'll get an orb from an orb flower coming down a waterfall. Progress onwards to the right, and put the lantern on the first box you see.
Walk across the cloud bridge to the purple windchime, and interact with it.
Rewind time, collect the lit lantern and move forwards to have the orb taken from you, and then continue across the cloud bridge, this time with an unlit lantern.
You will gain a second orb. Use it on the light bridge, and continue on.
Move to the windchime with the boy and interact with it. Use the girl to get the orb.
Interact with the windchime again. This will close the orb flower.
Move forwards, and have the girl place the orb on the box directly above the navy mug-shaped object.
Go across the cloud bridge.
Move up to the pedestal right underneath the huge telescope.
Using the pedestal underneath the telescope, adjust the landscape so that the moon is directly above the telescope and slightly to the right to remove the light orb from the lantern, like in the picture below:
Using the pedestal move the moon so it's directly in line with the telescope. You should see a white 'light switch' hanging from the sky.
Move forward and interact with the light switch. The moon will turn into a light orb.
Move all the way up to the top to the pedestal under the telescope. Move the moon all the way to the left that it will go;
the position in the picture below:
Rewind time to get the unlit lantern from the box, and move back across the cloud bridge up to the pedestal.
Just before climbing the ladder (as the boy grabs it), you'll be able to grab the moon into your lantern by positioning the girl in front of the moon, like in the picture below: