Yep those are the larger size of popsicle stick. You can generally find those in the craft section. Next you will need to pick some craft paints. I was sent some bright colors from the Americana collection by DecoArt so I used those.
Now I talked about doing these plant markers two ways. First you can make them plain painted with the words painted on them with a paint pen. Second you can make them chalkboard plant markers. I would recommend painting on the words if these are going to be outside. The chalkboard is amazing if they are going to be inside however. If you are going to do the chalkboard version, you will need some Clear Chalkboard Coating from DecoArt as well.
Now let the kids paint the popsicle sticks on both sides and allow to dry. Then if you are using the chalkboard coating, apply it per the package directions and allow to dry. You will then need to condition the surface with chalk as shown below. All of these steps are easy enough for a child to complete for mom.