Stackable pearl/hobby plate

So I have 3 small children aged 3, 3 and 4! There is always a fight and everyone have different kinds of patience when it comes to hobby activities etc AND temper hahah So I wanted to make a small but big enough pearl tray for them so they can sort and have individual plates that are theirs and theirs only Why are they on the “shallower side” ? (Incase you want them higher, scale Z axis BUT remember to scale conection pins Y axis if you use my 3MF) The reason for them being “on the shallower side” is due to the fact that kids want things FULL, So I made them high enough to fit a good amount of pearls and appear super full but still if the anger came to mind and one through them on the floor, you dont have to clean up 2000 pearls :D I also made dem stackable on a conection pin that you glue into place so you can stack them! Why are the conector pins not square or bigger?My reasoing with this is I wanted to save some space AND I didnt want the trays to be super hard to detach from eachot