As a dad, who would like my kids to be able to use this, I also think that the copy and paste features should be made into regular buttons so you don't have to RIGHT click, or in the case of a macbook with a trackpad, Control and tap on trackpad. RIght clicking is not a very discoverable or friendly feature for this friendly app.
A much friendlier set of icons would have been an UP Arrow pointing TO a clipboard and a DOWN arrow point from the clipboard to your grid.