I think these were probably water balloons. The idea is that all of those straws are connected to a single garden hose fill adaptor, so the whole bunch of balloons can be filled at once. (example: https://www.aliexpress.com/item/33011481532.html)

I abhor the single-use plastic, but at the same time water balloons are just fun in the summer. If paintballs can be made biodegradable (they're gelatin), maybe there's hope for water balloons, too.