If you're going to put buttons on everything, be sure you glue or stitch the hell out if them. V might not try, but if Andrew were at that party, he'd make it his personal mission to eat every last one.
**Steps off soapbox and becomes fun muppet again. **
It would be really easy to decorate cookies to look like buttons and fondant buttons are super easy to make if you wanted to decorate cupcakes. You could decorate photo frames with buttons and display your favourite pictures from V's first year. You could make a button bouquet to fill a vase.
Sounds like you'll be busy making crafts! Have fun!
This is in Sam's nursery. I got the idea from pinterest. I suppose this wouldn't be something for the kiddos to do but maybe you can have your moms make a button tree as an activity that they can take home? You can provide the canvas and paint or have the trees already painted and they can just glue on the buttons.
Sorry if someone already mentioned it here, I haven't read through first.