Since this is for a 5th grade graduation, can I suggest cupcakes instead? If this is for a party at school after the ceremony (my experience last year and the year before), the kids are running around and having a great time with friends, teachers and parents - no one at last year’s celebration was very interested in cake slices. The cookies, cupcakes and individual fruit skewers were the first things to go - people could pick up a cookie and walk around with it; you didn’t need a fork, plate, napkin, etc. It’s less of a mess - no cutting, plating, etc. Pick up a cupcake and go!
Before the display gets devoured, you might even be able to line up the cupcakes and spell out something - or use frosting in the appropriate school colors (hopefully not black and red! Dark colors can stain teeth/tongues, which in the 5th grade might be seen as cool…!)
If the cupcakes or other individually portioned goodies won’t work for this celebration, I’d say go with the rectangular cakes, baked in 2” or 2.5” pans, split once (so there’s one layer of filling in the cake) and do several so you can have one chocolate, one vanilla, one yellow…. variety is the spice of life!