But it wasn't always that way. Here's a 1415 painting as proof that once it was very right and proper for a male baby to be kitted out in pink.
This altar panel by Lorenzo Marco is called The Virgin and Child Enthroned, and it hangs today in the National Art Gallery in Edinburgh.
Mary is in her usual blue robes while young Jesus is rocking it in a rosy hue. Pink was pretty usual then for men. Leonardo da Vinci apparently used to stride around Florence in a pink robe and liked jasper jewellery and Cordoba leather boots. Quite the cool dresser, he was.
It was only in the 20th century that somehow the 'blue for boys' rule became commonplace. Around the turn of the century most infants were dressed for best in white, and girls and boys wore dresses well into childhood. Little boys didn't get into trousers until about six or seven.
Then colours crept in, and as late as 1918 the US Ladies' Home Journal said, "The generally accepted rule is pink for the boys, and blue for the girls. The reason is that pink, being a more decided and stronger color, is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl."
It was post World War II that saw a huge surge of pink for females, as femininity became prized after the grim war years and pink was seen to best exemplify it.
There's plenty more in this article about J B Paoletti, author of a book called Pink and Blue: telling the boys from the girls in America.
PS Blue for the Virgin Mary wasn't always the trend in European painting. It was only the importation of brilliant blue lapis lazuli in Renaissance times that gave artists a bright and solid blue to play with. It was very expensive – and of course only the priciest paint could be lavished on Mary's wardrobe. Hence the blue we associate with her now, even though in earlier times her robe was usually painted in duller shades of green and brown.