Koushaku-ke no Aisare Nise Youjo

https://www.cmoa.jp/title/321214/
Sophia, the daughter of a viscount’s family, lived a harsh life trapped in a tower of mages — working day and night until she nearly collapsed from exhaustion. But the worst part? She discovered that the very mage she trusted the most — the one who gave her strength to endure — was actually the one secretly ordering her torment. Devastated and heartbroken, Sophia decided to escape that hell. But escaping wasn’t easy… so she resorted to one desperate solution: creating a potion that would turn her into a small child! And it worked. With her youthful appearance restored, she fled far from the tower — and stumbled into a life she never could have imagined. A powerful ducal family took her in as their adopted daughter, showering her with love and affection she had never known. A gentle father, a doting older brother who spoils her endlessly… And best of all? No more work! But peace never lasts forever. One day, a young boy her age named Adam, the son of another duke, appears before her — and starts approaching her with mysterious kindness. And so begins a heartwarming and hilarious daily life between a runaway girl turned child… and a noble boy with secrets of his own, in a world full of love, pampering, and charming little adventures.