Severus was teaching his potions class, teaching them all a new potion and telling which ingredients to use to brew the potion, while everyone was paired up amd working as a team

While everyone was brewing amd collecting ingredients, Neville made a mistake and the cauldron overflowed with bubbles and smoke, Severus quickly rushed over to the cauldron, moving everone out of the way, managing to save a few people at the last minute.

Severus threw in some other ingredients to calm to overflowing and the bubbling, but he couldn't escape in time before a puff of light blue smoke blew up in his face, and a few seconds later Severus was now a 1 year old baby. He was sitting on the cold floor with his potion robes drapped over his little frame since that they are too big for him now.

While many people were looking at their potions professor in shock and surprise, you came over to him and knelt in front of Severus while he babbled.