Remove the high chair tray that needs replacement. Use a screwdriver and adjustable wrench to remove the hardware that holds the tray in place. Set the hardware aside for use on the replacement tray.
Place the old tray on top of the furniture grade plywood panel. Trace the outline of the tray onto the panel.
Cut the outline of the tray out of the plywood panel. Use a band saw to make the cut.
Rout around the outside edge on both sides of the plywood to create a 1/2-inch rounded edge on the tray.
Sand the surface and edges of the tray with fine-grit sandpaper. The tray should be completely smooth.
Drill any holes that are necessary for the installation hardware. Refer to the old tray for proper size and placement.
Apply a wood finish to match the finish on the high chair. Allow the finish to dry before handling.
Align the tray in place on the high chair. Fasten the tray to the high chair with the hardware that you set aside.