If no new bottle of supplements (like a fish oil gone rancid for example) and they’re eating from ALL of the same batches of proteins (so you know nothing went bad or got slightly undercooked), I would suspect a virus.
Focus on extra water/salt intake!
I always use the flushable wipes from Sam’s club. Let the Charmin extra strong toilet paper do the initial work, then finish smooth with a couple wipes. ‘Clean butt, happy butt!’ I always tell my toddler when I change him
You gotta keep wipes in the gym bag too!