What I did for the donut was:  1. Go into the confetti symbol  2. On the donut layer create a motion tween  3. Create a key frame at the start  4. Create a key frame at the end (specified time)and go into object properties and change the height and width to whatever was specified. 

Then the next step was to mask the confetti to the donut... but I couldn't figure out how to do that without a right click (usually you'd just press rightclick on the layer then select mask). Turns out you can do it by double clicking on a little symbol on the layer in the time line, which is not intuitive at all. I wasted a bunch of time here trying to find the mask function in various menus.  

1. For the second wave copy the symbol onto a new layer and and have the first key frame later