Tip: dont use the symmetry tool on the backgrounds! It looks really bad when both the characters and backround is just the same thing twice. The lineart is a bit messy in some places like on the lower half of the cloud. Cleaning it up doesnt take that much time so just go over the drawing and check it, it really makes the whole thing look better. It could use a bit more shading, I see that you begin on the top of the bottom cloud and their skin, but left the rest flat, which isnt the best decision knowing that its really easy to shade clounds in the way to make them look fluffy. I really like their faces, especially the eyes and the blush on their cheeks!
I hope it helps at least a little, even if my english isnt the best ;p

Her smiles tells me everything.
I like your style of the lineart tho the bow on her chest really bugs me, it looks like its badly copy pasted here, but over all the drawing is really nice <3