For Lego, they created a line of Legos specifically for girls called “Lego Friends”. From what I have read, the sets mainly involve things like cafes, beauty shops, and homes. The sets are populated by “ladyfigs”, which are taller and curvier than the standard “minifigs” (which are mostly male if they are clearly gendered). Basically, it seems like the Legos marketed towards girls are separated from all the other Lego City sets which strongly indicates that everything else is assumed to be “for boys”. BoingBoing has covered Lego and gender before: http://boingboing.net/2012/05/15/history-of-gendering-in-lego.html and http://boingboing.net/2011/12/14/134329.html
I am not sure if I would really look at K’nex and think “gender neutral”. Of the regular building sets, they have a lot that seem geared towards boys: Robo-Creatures (Robo-smash, Robo-sting, Robo-strike), Transport Chopper, 4-Wheel Drive Truck, Strike Force Bomber, Rally Sport Racer, and a K’NEXosaurus Rex. The amusement park ones seem fairly gender neutral. Of the “specialty” themes, I would have said that maybe the Thrill Rides was gender neutral, but of the eight that showed the front/back of the box, seven of them had boys pictured (the other had no kids shown). The Nascar line has at least one female racer, but she is one of the people who only apparently has one set to her name (some of the other guys have transporter rigs, pit crews, etc.). The Roary the Racing Car line does not feature any of the female characters from the show.
TinkerToys seems to do a better job and aiming to both boys and girls since their products have three with girls on the box versus five with boys on the box. The boys are on the transit building set, the vehicles building set, the “big top”/circus building set and the “SuperTink” building set (heroic adventures). One of the girls is on the animal building set, but another girl is on a box labelled “TinkerToys Pink” (build a castle, a flower, and a cat). I think, unfortunately, that if a little girl saw all these sets lined up, she would think that the pink box was aimed at her so by default all the others were aimed at boys.
I think it would be great if engineering toy brands:
(1) Did not indicate that only certain boxes were “for girls” by making one of them the “pink box”.
(2) Showed both boys and girls playing with the toys.
(3) Created a variety of sets (some geared towards stereotypical boys, some towards stereotypical girls, some gender neutral) but did not color-code the sets with stereotypical colors.
(4) Included multiple colors in all their sets instead of gender-neutral/“boy” colors for gender neutral and “boy” sets, but only “girl” colors for “girl” sets.