Now I have found a comment by Rebecca herself from many years later (1847). This time it is a great-nephew who has been breeched around the time of his third birthday. Rebecca had received a visit from her niece Miriam and her family, from Savannah, a few months previous to the letter. Miriam's son Gratz Cohen was still wearing the skirts of a baby at the time. Rebecca's response to the news that he had started wearing trousers is a mix of sentiment, good sense and sound observation:
"The infantile costume became him so well that I was unwilling to have it changed. There is so much more freedom in the motions of a child's limbs in the loose dress than when buttoned up in trousers which has neither grace nor ease, that I wonder parents do not prefer to keep them longer on -- but the [boast?] of man's prerogative is assumed with his change of dress -- and little boys fancy they are becoming men, much faster as soon as they throw off [their] frocks!"
(The letter is in the Miriam Gratz Moses Cohen Collection, No.02639, the Southern Historical Collection, the University of North Carolina at Chapel Hill.)