"sodis" is the swiss acronym for filling a soda container with water then leaving it to sun for a few hours to create drinkable water. This awesome idea is aimed at developing worlders; the documentation [link] says it prevents diarrhea
I think a major source of developing world lethal diarrhea might
be hand mouth contact as well as teething on soiled objects; grandiosely, there might be as many toddler lives saved with a teething chew object on a lanyard (kind of like soap on a rope) as from the water they drink.
this idea is as minimally complicated as possible but might reduce ground dirt contaminated hand to mouth activity muchly
I think flavored, or flavorable rubber or wood, would be effective.
I was chewing on rubber electrical cords or my shirtsleeves at age seven; it is possible developing worlders give their kids rags to chew on (yummy sleeves) a research project would be determine if natural fiber or polyester is better at minimizing germs; rag on a lanyard might minimize hand to mouth disease transmission
possible absorptive core to minimize surface gooiness
if a lanyard is only with older kids then an around the chest with an armloop version might go with babies as toysrus has baby bikinis like that, just one armloop is sufficient to remove most hazards. The hazard difference between bib or lanyard shape are a puzzle