Summer time is the perfect time for letting toddlers paint. Just bring it outside! Fill a little wading pool nearby, use washable tempera paints, and you are good to go. Put them in their little swim diaper or swimsuit, give them a brush and a piece of paper and watch what they create.
I made this handy little outdoor easel and paint tray in less than 15 minutes. Take a large box - this one was an old diaper box. Cut off the two side panels (the small ends). Then flip the box inside out and duct tape it into a triangle shape:
Set it up on a low bench or chair out in the grass, and use a large rock or two to hold it down by placing them inside the triangle. Use masking tape to attach a large piece of paper. We almost always use freezer paper as it is shiny on one side, which is great for fingerpainting, and matte on the other side, which is great for just about everything else.
For the paint tray, I used a small 6-cup muffin tin. Originally I planned to just save the paint in it and add more as needed. However, this particular one started to rust (it was from the dollar store, so I'm not sure if that would happen with all of them, or those that are coated). So now we use small plastic tubs from individual size apple sauce and I attached them to the muffin cups with tacky putty - the kind you use to hang posters, etc. Cleaning them is super easy, though to be honest, we don't really clean them up very often. I just cover everything with aluminum foil and we bring them out whenever we want to paint. If the paint has thickened a little bit, just add a little water, or a little more paint and mix it up. It's easy for a toddler to use because the weight of the muffin pan keeps the paint stable while they dip the brushes in. Regular cups are easy to tip over, but we've used this for a few months now and haven't had a single spill! We have another one that we use for liquid watercolors, and it works just as well.
So go paint with your kids! And have a beautiful day! ;)