Sometimes Pinterest is great. (Okay, this was actually just a google image search for "kids' robin craft" that looked easy enough to do...but I'm sure it's on Pinterest somewhere...)
And sometimes it's not.
Just saying, sometimes it might just be cheaper to go to the dollar store and buy yourself some cheap water color paints for a toddler to play with instead of making your own from corn starch and baking soda and vinegar. The watercolors I just tried to make worked well... They just didn't show up at all after drying. And they took more work than forking out a whole dollar.