I prepared this work before the road trip, but I didn't put it out on the shelf yet because I wanted it to still be interesting when we were on the road. In the car, we didn't use a tray. I held the bowl full of buttons and she held the container with the slot. She took each button from the bowl one by one and put it into the slot. I made sure not to open the container until all the buttons were inside -- if I opened it too early, she would start insisting that I open it after she put in each button.. Now that we're home, it sits on her practical life shelf on a tray, and she frequently takes it from the shelf and brings it to her table.
The best part about this homemade work -- I had to eat all the Piroulines before I could make it. Oh, the sacrifices we make for our children. :)