Charlaquin
Goblin Queen (She/Her/Hers)
One way to differentiate between Small and Medium characters might be to use the optional Tumble and Overrun bonus actions from the DMG. Creatures already have advantage on the Athletics check to Overrun if they’re larger than the target and disadvantage if they’re smaller. Reverse that for the Acrobatics check for Tumble and you’ve got a nice, symmetrical set of size-based advantages and disadvantages.