I found a very easy envelope template to use for this. I made the envelopes from construction paper of different colors. Gluing the sides and then the bottom (I cut off the top). I made mine 4.5 inches tall and 2.5 inches wide.

You can use colored craft sticks to let your child match them to the envelopes. You can also use these as a counting game by making number cards to decide how many items go into each envelope.