It sounded like one pup was thought to have gotten most or all of it. If that were the case, she would have almost certainly bloated up. Now it sounds like they all shared it. There is no way in heck that I'd be taking all 4 to the ER for something like this unless what they got was toxic.
Hard plastic would concern me much more than soft because it can't conform to the shape of the intestines and is much less likely to pass. You'll see signs if your dogs are obstructing. No reason to panic. Even some loose stool could be normal after this (but of course always check with your vet). Any vomiting, esp. of food, and any inappetance = immediate vet visit as does lethargy or gum color that is off.
And yes, small meals 4-6 times a day and giving bread is pretty much standard of care for when something is ingested that is sharp. I would not overdo the bread though.
Most YTers would be appalled to see the list of things that Rylee has eaten --- all within a week of each other. His vet knew about it. We didn't go to the ER because we knew what the ER was going to do and it just wasn't necessary. And I don't religiously check poop either. So it may or may not have come out. Thinking he might have the ability to digest blankets though. Cool, eh? Ohhh some comforter fluff came out though. That was very noticable. He was about to get a basket muzzle bc of his habit, but has cut down. lol.
I think they say don't come in a lot because many things that are thought to be an emergency...aren't...even if the owner insists they are. And even if the vet does end up treating/testing at the ER, that still doesn't make it an emergency. It just makes the vet keep their sanity by making sure the owner is comfortable.

And then on the other side of that there are many emergencies everyday that owners ignore.