A 3 year old has no clue what a boy or girl even is. So its one thing to just play along until the child gets older and understands, but even doing it that will just confuse the kid even more by the time he is able to understand whats happening. So if a kid has no idea whats happening and the adult is going along with it then yes that is encouraged behavior.Â
At 3 years old, kids want to be firetrucks and mermaids and princesses. They know same about sexuality so the adult going with it is just harmful to the kid.
"Children as young as 2 years learn to label themselves as a boy or a girl, and by age 4–5, are able to understand that gender is a stable and lasting aspect of their identity.40 Boys and girls have group differences in toy preference by as early as 12 months and can label other children as boys or girls by age 2.41"
Research seems to indicate that 3 year olds are not that far off from the normal age by which children understand the concept of gender. What information do you have that indicates otherwise?