Button egg carton busy "bag"

I just made this with my 2 and 3 yo's.  Michael's had little containers of buttons for $1.  I used extra craft thread and needle to string the buttons.  Then poked through the bottoms of the cups and tied the strings in a knot.  It makes a loop with the buttons in the cups.  The kids can move the appropriate number of buttons into the labeled cups.  

My big goal was to not have a million loose buttons all over the place.  Yes, eventually they will pull these strings through the styrofoam, but the buttons will still be knotted on the string.