This is how I would tweek your finger painting one to be a child centered activity rather then an adult centered activity and to involved all the domains.
Three Year Olds
1. Finger Painting
Goal: Understanding the concept of area, manipulation of fingers and hands, and use their imagination.
great goal, I might add freely chooses materials for fingerpainting, improves speech and finger movement, identifies colors to incorporate three areas.
Materials: Finger paints in various colors, paint shirts, white paper.
maybe add different types of papers - finger paint paper, construction paper, wrapping paper, etc the markings created appear different on different surfaces - so just having it available in the art center for children to freely choose the materials and colors. Also how do you store the paint for the kids? I'm thinking some kind of tray or dish (We use gerber graduates trays and wash them for children to use when painting and gluing but some licensing agencies do not allow that.
Strategy: Start off by showing them an example of what to do. They will most likely take off on their own. Redirect if they get off task. Do not mess with their work by adding things.
three year olds will know how to finger paint! I highly doubt you'd need an example for them - I work with toddlers and do not need an example, they just dip there fingers into the paint tray. I also doubt they'll get off task, or mess up their work on their own terms - I just as a teacher wouldn't have the children create the art in a way they did not desire to. I would name the colors and encourage the children to identify colors as they mix them together, use fine motor skills to paint - fingers and wrist rather then whole arm movements. Also, of course having various colors and paper types available helps them to freely choose materials to express themselves. I might say "encourage children to choose a desired paper, and paint color(s). Encourage children to identify the colors, and notice changes as they mix the colors together while increasing motor control of wrist and fingers (Fine motor)."
It is really simple to incorporate cognitive, physical, and creative domains in activities. Cognitive includes anything in the brain - and since they didn't list language as a domain I would throw language under cognitive so you can add new and more complex words to jsut about any activity. It might be helpful to google some developmental checklists to find goals for your assignment. I just pulled some goals from my DD's checklist since she's three. If you need any more help please PM me. I love doing stuff like this