Framed Antique Portrait of a Child

I think it is of a little boy but in the 19th century they tended to dress little boys unisex. I just checked Wikipedia and they think:

Breeching little boys The main reason for keeping boys in dresses was toilet training, or the lack thereof. The change was probably made once boys had reached the age when they could easily undo the rather complicated fastenings of many early modern breeches and trousers.