[Macha]

> although dresses were worn much longer than necessary for toilet training, so they must have had another purpose or benefit too

Easier to reuse across a wider range of child sizes (either the same child over time, or siblings). You don’t need to worry about e.g. leg diameter or crotch/knee heights like you would with trousers, so can get by basically just folding it to fit height and waist. In an era where people modified and repaired their own clothes more rather than having modern cheaper but more disposable clothes, that would matter more.