Your lesson sounds pretty good so far! I think you could deepen the content for your students by tweaking a few simple things.
I just recently read this article, and I think it'll help you add one more element to your KWL chart - the E (evidence), which is definitely appropriate for 4th graders. Check it out here: https://s3.amazonaws.com/nstacontent/sc0602_50.pdf?AWSAccessKeyId=AKIAIMRSQAV7P6X4QIKQ&Expires=1558551796&Signature=JoDunOrsrOcmxvPhM1dNuubtdL8%3d.
Try asking your students questions that get them thinking: How is this (item) "working" or "turning on"? What can you see happening? What can you not see happening? I could also suggest allowing your students to "experiment" by themselves first before/instead of telling them what they are going to do. This way, they are able to discover parts of the phenomena on their own, and you're not killing their wonder. Then, you could do your demonstration. For circuits, I would personally allow my students to explore with different types of circuits - basically, give them more than just one opportunity for them to get their hands on the materials.
Some other good evaluation/assessment strategies you could think of implementing are: having students create a drawing that depics what they think is happening inside the circuit, creating their own (additional) model, or you could use an Interactive Science Notebook.
Good luck on your circuit lesson, and happy teaching!