You don't need extra certifications. Most music certifications now are all-level. You just need to be ready with all that goes into each day. What is 1st grade doing, how is this 3rd grade class progressing, what numerous equipment will I need and use for each class/grade level...
I was not ready and didn't last very long, and returned to secondary band. I also wasn't into all the singing and childhood-type music.
I have a HUGE appreciation of what goes into elementary music know. I would not return unless I go through training and observing experienced and successful elem music teachers.
I wasn't good at it, not gonna deny it.