With Anne Fine's early reader (and Carnegie Medal nominee for 1989) Bill's New Frock, one morning, main protagonist Bill Simpson wakes up to find that he has suddenly physically been transformed into a girl (although internally, emotionally, Bill actually still feels that he is a boy and not at all a girl). But Bill's mother, she is totally unperturbed, seems to just accept Bill suddenly being a girl and then forces her son to put on a pretty and frilly pink frock (a pink dress in American English) and hence the book title being Bill's New Frock. And once at school, Bill is also approached by everyone as a girl, is supposed to behave sedately, quietly and must realise and come to term with the reality that girls are (even in the late 20th century when Bill's New Frock is taking place) seen very differently than boys, that for example girls are expected to keep their clothes neat, tidy and frilly whilst boys are allowed to be rowdy and often even rather messy with no or at least not much overt criticism.
Now and in my humble opinion Bill's New Frock first and foremost has Anne Fine providing important and essential insight into gender differences and gender stratification and is textually demonstrating that the traditional school day is actually very much different and also rather inherently lacking fairness for girls, with them supposedly being responsible, neat and tidy, but physically weak and lacking, and boys as inherently scruffy and more violent (but that this violence is actually often seen as something rather acceptable for boys but not at all for girls, who are supposed to be dainty and never losing their cool, their temper), and that Bill Simpson suddenly has to adhere to entrenched and problematic stereotypes just because he now resembles a girl on the outside even though he still totally feels like a boy in his heart, on the inside.
And no, Bill's New Frock is thus not one of those "boy wearing a dress" type of tales, as it is clearly shown by Anne Fine that Bill Simpson does not want to at all wear that new frock, that new dress, and that he totally feels like a boy and not like the girl he physically now looks like, presenting a delightful, easy reading and also thought-provoking account about the necessity and the importance of basically and generally getting rid of gender-based stereotypes (for everyone) and allowing children to behave according to their own wants and desires regarding gender (regarding what children are wearing, what they enjoy doing, how their are approached and communicated with, basically what children's lives and their feelings are about gender and that this needs to be respected and universally so). But while Bill's New Frock is also not yet in my opinion a novel about a trans-gender child, well, the feelings Bill Simpson has, how he reacts and how those around him both adults and children (his classmates) react and consider him, it does for me kind of textually seem like someone, like Bill is in Bill's New Frock feeling caught in one gender but believing that this gender designation just does not work.