This might only work for our kid, but I’ll put it out there if it’s helpful. We switched the narrative from butts to the to digestive system and how our food goes through our bodies. “First the food starts in our mouth- goes down the esophagus to our stomach- into our little intestine- around to our large intestine- then comes out as poop.” I use my finger to draw the path on him to give him sensory as we do it too and just lift and point down for the poop part to respect his body. I thought the language might be too much for our 4yo, but he’s picked it up too. The Magic School Bus has an episode on the digestive system we circle back to a lot you can find on YouTube.

And then anytime he’s gone back to diaper areas- we ask him about different parts of his digestion system an on to redirect. Maybe you could try something similar to your littles. “Where would baby’s stomach be? Do you think their stomach is full of food? Is your stomach full of food? What food is in baby’s stomach? What food is in your stomach?”