Hamtaro S01 E216 The Changing Mirror

"Little Hamsters, Big Adventures."

Elder Ham and Auntie Viv are surprised that hamsters can eat sweets, but they happily join the Ham-Hams playing in Sweet Paradise, but then a magic mirror makes Auntie Viv and Bijou switch places. When Hamtaro tries to figure a way to change them back to themselves, he gets himself switched with Elder Ham.