When thinking about toddler art curriculum I like to think of it in the following categories (again to make sure I am providing a broad range of experiences):
Painting * Drawing * Sculpture * Printing (overlaps a lot with painting) * Textile Arts * Collage * Photography * Crafts * Digital Art
I think painting is the most fun so here is the list of every toddler painting activity I could think of and find. Beyond experimenting with different kinds of paint (finger, watercolor, tempera, glitter, biocolor, powder, fabric, etc.) and brushes here are some other fun activities you can do with toddlers:
Fingerpaint with pudding, yogurt or cool whip - color with food coloring or do this in the shower.
Shaving Cream Painting - color with kool-aid or tempera paint. Make design and then press paper on top of it. There are lots of cool marbled effects you can get with shaving cream and paint.
Kool-aid Paint - Mix 2 tablespoons of water with one packet of kool-aid and paint. When dry is scratch and sniff!
Texture Paste - Equal parts flour and salt, mixed with a little water and tempera paint to make a thin or thicker paste
Painting & Printing with a variety of objects: feathers, combs, q-tips, potato masher, toothbrush, bath poofs, etc. Anything with fun textures.
Stamp & Sponge Painting
Crayon Relief - Color a picture with crayons and then paint over it with watered down tempera paint. Works beautifully for under the sea drawings painted over with blue watered down paint. Also you can use white crayons to create a design and then paint over it
Make stamp pads by watering down tempera paint on a wet sponge
Ball Painting: drop dabs of paint on a paper in a box or lid and then roll marbles or balls through it to create a design
Bubble Painting: Add food coloring to bubble mix and blow bubbles onto paper. For older children you can use paint in the bubbles.
String Painting: Tie things to string and drag or just drag string
Bingo Markers or bingo marker containers from school supply store to fill with washable paint
Spin Art - Put paper in an old salad spinner and drop in different colors of paint - then spin. Very messy.
Frozen Paint - Mix tempera paint and water then freeze in ice cube trays, paper cups, or popscicle trays. You can also freeze BioColor
Food Prints - cut up hard different fruits and veggies to make stamps. Apples and corn are the most common.
Spray Bottle Paint - Watered down paint in spray bottles. Fun to put a shape down on the paper and spray over then remove the shape, layer colors etc.
Snow Painting - Use spray bottles filled with water and food coloring to paint snow.
Dropper Painting - Use droppers filled with paint or watered down paint
Rain - Put freshly painted paper in the rain for a few seconds
Coffee Filter Painting - Use bingo stampers, spray bottle painting, or dropper painting. Once dry cut out shapes. Makes a tie-dye effect. This is how you make the wing portion of the popular clothes-pin butterfly.
Magnetic Marble Painting - Bin or box propped up on the sides. Paper in the bottom of box with paint splattered around then put magnetic marbles on top of the paper. Use a magnetic wand underneath the box the move the marbles around and paint. You can buy the wands for about $1 and 20 marbles for about $6 through Discount School Supply.
Car Painting - Use toy cars and trucks to create tracks on the paper.
Animal Tracks - Use toy animals to make foot prints on the paper
Nature Painting - Using shells, leaves, sticks, etc. as stamps
Painting Life Size Objects - Trace your childs body, draw a life-size version on their favorite car or bike, etc. on a big roll of paper and have them paint the huge shape.
Body Prints - Besides just printing with hands use feet, elbows, wrists, belly, cheek, etc.
Sidewalk Paint - Make your own! http://www.petitelefant.com/homemade-sidewalk-paint/
SOURCE NOTE: The ideas I didn't add from memory were mostly pulled from answers to a forum thread on Baby Center.com that I just can't get back to for some reason.
More toddler curriculum ideas here or under the category 'toddler curriculum'
Can you think of any more???