In the 1970’s Lego sets came with the enclosed letter:
The urge to create is equally strong in all children. Boys and girls. It’s imagination that counts. Not skill. You build whatever comes into your head, the way you want it. A bed or a truck. A doll’s house or a spaceship. A lot of boys like doll houses. They’re more human than spaceships. A lot of girls prefer spaceships. They’re more exciting than dollhouses. The most important thing is to put the right material in their hands and let them create whatever appeals to them.