Just an FYI, most of my art projects are completed outside...it helps with the clean up and I don't stress about the mess. I bought one of those plastic tables for $2 at Goodwill and it stays outside as a craft table. Since our back porch is covered and has a fan it's usually cool enough.
It can be a little messy, but finger paints and side walk chalk are fun.
I also used to pour glue into a bowl and give my son a big bowl of cotton bowls. He could dip the cotton ball in to the glue and stick it to paper. At Christmas time I printed Santa pictures and he glued beards. At Easter it was the Easter bunny's tail. When it's cold snowmen...you get the idea. It was messy but lots of fun!
I also keep dyed pasta on hand.You use alcohol and food coloring and dye pasta. It can be used for stringing which helps with hand eye coordination (the larger the hole the better). It can also be used to glue on to paper.
A salad spinner can double as spin art. I bought a super cheap one at Target, you don't need or want anything fancy. I put a coffee filter in the bowl. The kids pick the colors and you put little dabs of it on the paper. The kids spin it and it makes the colors spread. Sometimes we stop, check it and add more colors. I have used a bunch of different paints, but I always make sure they are washable, so clothes don't get ruined.
Play dough is fun. We make our own...that's a craft project in and of itself. We just refill the commercial play doh containers with our home made stuff. It's cheap and easy. I always cover the kitchen counter with newspaper. My son measures the flour and it helps keep the clean up easier.'
Stamps...we have had a lot of fun with stamps.
We also enjoy doing impressions. When we go for walks, we look for "treasures". We come home and put the leaves and flowers under the paper. Using the side of a crayon you color and it leaves an impression of what's underneath.
HTH! Have fun!