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.

I'd guess they are water balloons from the description. My wife has purchased those from Costco. They are e easy to fill up all at once. They do make an unholy mess that takes the kids a while to pick up.

Under the sunny conditions that facilitate their use, they bake onto surfaces. It's horrendous when you find a bit that wasn't seen, but just another childhood/childrearing experience.