Yes, this is a big taboo that still exists, and I believe that the way to deal with it will vary according to age and circumstance.
The curiosity of children is one of their main characteristics. So, it is common for boys to play with dolls and girls to play with a ball or a cart. Parents or guardians are more inclined to set boundaries for conforming to societal acceptance.
Regarding clothing, some girls like a more stripped-down style: pants or shorts instead of skirts and shirts instead of dresses. In general, society is not bothered by this, accepting it as normal. In many cases, they may wear skirts and dresses when they grow up.
And yet... there are boys that are curious about wearing dresses and skirts... but this is still taboo.
The DSM-V, a manual that lists mental illnesses and disorders, defines "gender dysphoria" and does indicate that on average for every ten children who (at some point) did not identify with their biological sex, more than half of them will identify with their biological sex as they reach adolescence or move into adulthood.
We go through puberty. This biological process moves our transition from childhood to adolescence. It is the process that begins to accentuate the differences between boys and girls.
The boys gain muscle, beard growth, and a thick voice. Girls start to have a more defined waist, watch their hips grow, discover physical changes, and experience breast development.
Hormones are responsible for these physical changes and also for the behavioral changes of boys and girls. During the transition, the accentuation of differences changes the way in which boys and girls see one another.
Personally, I remember at age 12 noticing the girls at school started wearing bras. I was curious and decided to try my sister's bra. I got dressed and enjoyed the experience. Sometimes, I went to school wearing a bra.
Interestingly, my curiosity at the time about girl's clothing was limited to bras. It would be later that my curiosity expanded to panties and other items...
And... what if my sister or my parents had discovered my bra-wearing? How would they have reacted?
I can relate this to how I might react if I were to have a son and then discover he is wearing his sister's or mother's bra, or that he wants to wear dresses and other girl's clothing... First, I would try to find out why he wanted to do so and follow an approach that would vary based on their age.
If he really wanted to try it on, I wouldn't mind. I would consider buying a dress, panties, or even a bra for him if that is what he wanted. I would not encourage him, but I also wouldn't try to suppress his stated desires.
There might need to be boundaries put in place to protect him. He would have to understand that society is (not yet) ready to understand certain taboos. I think it is more important that he has his own clothes and does not resort to sneaking items from his mother or sisters. Even though many sisters of similar age and size share their dresses.
There are some reports of mothers who put their children in dresses as a way to discipline them. I don't know if that makes sense, although I can see how the experience might help boys to be less macho in the future.
I don't want my sons or daughters to be suppressed, as I suppressed myself. I will not scold them if they want to wear something different, just as I won't encourage them. I will support their choices. I believe that having gone through this myself will allow me to have more empathy and make it easier to deal with it. I think this is true for our generation now as compared to our parents or grandparents, for example.
It is important to remember that each case is different and that the child's age must be considered, he cannot do something that does not match his age. There needs to be respect so that it may run its course correctly in all aspects.
It should be noted that in most cases, boys and girls who try on clothes of the opposite sex are just participating in childish curiosity - and this desire soon disappears. Only a small part of those cases become linked to the practice of crossdressing or transsexuality.
Did you start crossdressing at a young age? Did your parents know? How did they handle it?
What would you do if your sons or daughters liked to crossdress?