I actually saw this a few years ago in Korean (남주의 엄마가 되어버렸다), but there's now an official English release so, I decided to share in case someone didn't know about it. Long story but she mistakenly drinks a shrinking potion, starts at Chapter 62 and she remains small until Chapter 65. Nothing spicy at all, just the male character and his son fawning over her cuteness.