2. Boys sometimes wore bands (http://en.wikipedia.org/wiki/Bands_(neckwear) ). Due to their frequent use of lace they often are perceived as feminine today, but were perceived as masculine at the time. You can sort of see that on Roosevelt in the linked article. Some clearer examples are visible in the Wikipedia gallery of unbreeched boys: http://en.wikipedia.org/wiki/Breeching_(boys)#Gallery
Source, unfortunately paywalled (and it's a very minor part of the article, so not necessarily worth digging up unless you're interested in the main article subject): http://www.jstor.org/stable/1923418
Both of those gender markers look like they would be easy to alter with a bit of sewing, so the idea that clothing is gender neutral to make reuse easier still stands.
1. Boys more often had square collars. For example, if you look at http://commons.wikimedia.org/wiki/File:The_children_of_Charl..., the girl on the left has a rounded collar, while the boy 2nd-from-left has a squared-off collar.
2. Boys sometimes wore bands (http://en.wikipedia.org/wiki/Bands_(neckwear) ). Due to their frequent use of lace they often are perceived as feminine today, but were perceived as masculine at the time. You can sort of see that on Roosevelt in the linked article. Some clearer examples are visible in the Wikipedia gallery of unbreeched boys: http://en.wikipedia.org/wiki/Breeching_(boys)#Gallery
Source, unfortunately paywalled (and it's a very minor part of the article, so not necessarily worth digging up unless you're interested in the main article subject): http://www.jstor.org/stable/1923418