For this activity, you need to use blue, orange, and yellow construction paper. You would also need to use a single hole puncher.
On a piece of blue construction paper, draw a square (in a size that will fit inside the ziplock bag) with wiggly lines. Ask the child to cut the square that you drew and stay within the wiggly lines (thickness of the line depends on the child’s skills and development).
Draw a fish on the orange or yellow paper and have the child cut it out. Depending on the child’s skills, you can have the child trace a picture of a fish or draw his own fish.
Glue the fish onto the blue sheet. Ask the child to draw eyes, fins, gills, and mouth on the fish and add any plants on the blue paper. Use a hole punch to punch bubbles in the blue paper (coming out of the mouth of the fish and above). Place the blue sheet into the ziplock bag. Place the oats on the table or in a small shallow plate and ask the child to pinch the oats and drop into the bag, to represent the floor of the tank. Repeat this activity a few times, until there is enough oats on the bottom of the bag. Seal the bag nice and tight.