Have an adult or older child print and cut out a tree pattern, then trace it onto green felt with a felt tip marker. Do this twice so you have 2 identical tress.
Cut out a tree trunk - you can use a pattern but any square shape is fine. Then, trace and cut two identical trunks from brown felt.
Let the kids glue the two trunk pieces together. Then, glue the two tree pieces together with the end of the trunk inserted between the trees at the bottom.
Punch a hole in the top of the tree with a hole punch.
Insert the string through the hole, and tie it off in a knot to hang your ornament.
Let the kids place the buttons and/or beads on the tree and arrange them before gluing the pieces in place with craft glue. You can decorate one or both sides of the tree with buttons. Don't forget to add the child's name and the year you made it to the back of the ornament.