Crayons are a great art tool to use with toddlers, start at around 18 months. Using crayons to scribble with introduces them to art and improves hand coordination. To start with try the large, fatter crayons they will be easy for their little hands to grip and hold on to.
I love crayola kids' paint, it is washable and non toxic. Try a few painting projects with your baby/toddler it will be messy but allow them to explore the materials. Finger painting is a good project to start with and as they grow you can move onto using paint brushes.
Look for children's paint brushes like those pictured above, with a wide handle to make it easier to hold on to and control. And wide paint bristles to paint with. A tip for painting with young children tape the paper to the surface you're working on to prevent it from sliding all over, and use a thicker paper like watercolor paper so they don't go right through the paper and make holes.
I haven't used these, no spill paint cups, but I've seen them around and they look like a great idea for young children. The whole in the top is just big enough to get the paint brush through and this type looks like you could put the lid on to save the paint from drying up.
DIY paint holder I found this on pinterest and marked it to try with Cy sometime.
Chalk is another great everyday art material for toddlers to use. The size of this type of chalk is perfect for those little hands and the colors will really show up on blacktop. Or try an indoor project using a large piece of black poster board of them to color on. Get even craftier and make a chalkboard wall in your house for endless chalk fun. DIY chalk recipe.
And last but not least some of my favorite project ideas are from using found objects as art tools. This is perfect for young children it teaches them how art can be fun, incorporates play and allows them to express themselves. Last month I posted an everyday objects as art tools and featured the balloon painting, credit card painting and pedulum were both featured on The Crafty Crow blog.