Also you might go buy a bunch of inexpensive, soft washcloths to hand to parents of young kids, asking them to please use those for cleaning up the babies during diaper changes, or for spit-ups, rather than your good guest towels. And have a box of baby wipes as well- just put a note on the box saying to dispose of them in the waste basket, not the toilet. Parents should really provide these things themselves, but if they don't, or run out, they are likely to grab whatever is handy (your good white towels).
Big sponges, like the kind you would use to wash a car, are also great for cleaning up spills on the floor, rather than poeple using your kitchen or bathroom towels.