What manga is this girl shrinking into a child from? I've found this pretty cute image on the web, and I'm curious as to why the girl turned into a child, and what happens next. I've tried a reverse image search, but it didn't yield any satisfactory results. Does anyone here recognize this image? Could you please tell me where it comes from?
The pages shown in the question comes from the short story Heart no Kusuri in the shoujo manga collection Majo no Lesson by Natsumi Matsumoto.

The two-page spread of Heart no Kusuri one-shot:



And Chinese cover of Majo no Lesson:



Summary:


  Majo no Lesson is a collection of shoujo short stories including the title short about a girl who is always teased by the boy she likes about having long black hair like a witch. She actually is a witch and her hair holds her power, but she almost cuts it when she inadvertently seals the boy's voice away.




If you're wondering how I found the manga, I split the image in your question into two, then I did a Reverse Image Search, which led me to this page. I did an Image Search once again using the cover page. Voila!