Curse of Tir na Nóg

You attempt to curse a humanoid that you can see within range, channeling the time altering magics of the Feywild to return them to a juvenile state. The target must succeed on a Wisdom saving throw or be transformed into a childhood version of itself.  

For the duration of the spell, the target has disadvantage on all attack rolls, physical ability checks and physical saving throws, its weight is reduced to one third of normal and its size is decreased by one size category – from medium to small, for example. The target’s weapons and armour do not shrink to match its new size and remain unaffected by the spell.

A remove curse, greater restoration or wish spell cast on the target restores it to its true form.