I have seen people let their guests paint on a small canvas for the birthday recipient. This can be sweet, but it should be more of a gift, a favor, for the guests. While it can be sentimental, it isn’t something to give the birthday child.
At a young age, they may not understand its for someone else and the child may want to take it home. You can offer a few canvas’ so they can paint one for themselves and one for the birthday child. As for the adults or older children you can ask that the birthday child to keep it.
Just a note about asking for no presents: I have found that no matter how much you say NO PRESENTS you will be getting them anyways. It is something people like to do and like to pick out. Just keep that in mind.
I had a painting party for my daughters 2nd birthday. We bought bird houses for each child and they painted and decorated them. It was really a great party! We used sand pails from Michaels or AC Moore (dollar store or whatever) to put the houses in to bring home. They were wet and would need much more time to dry than the time at the party.
I would also buy glitter glue in bigger bottles and other things to stick on the canvas’ like beads and foam shapes. Use tempra paints so they wash out of clothes and try to find different kinds of brushes, use sponges and cut them into different shapes to paint with, glitter if your willing (thats why I like glitter glue) Tissue paper…anything! You can get the flat canvases in bulk too. Not too expensive. Dont forget to put the creator on the back before you let them start!