OMG, I'm sorry, but that is so funny! (except of course that it's not and I would not be highly amused if my kids did that, and it's certainly something they *coulda*, but, you know what I mean. Where do kids THINK of these ideas???)
If it were me I would s
tart doing some chemistry testing, particularly ammonia. Ammonia may well shoot up, and then nitrites (finally nitrates but not for some weeks prolly). If you detect ammonia levels going way up, there are things you can buy at the fish store to put into the filter chamber to remove ammonia or nitrites. (Zeolites, or some other thing, I really don't remember offhand, but if you go into the store and tell the guys "help, I need that stuff you put into the filter to get ammonia levels down", they will direct you to the right product). It's not super cheap (although not super pricey either) but can be awfully useful when you have a temporary "problem" like this that is beyond your ability to control with water changes and you don't want to just let the chips fall where they may.
I'm honestly not sure how much good a protein skimmer would do, I would not *thnk* it'd be all that helpful since there is not *that* much protein in milk anyhow but I suppose it might help with the resulting bacterial bloom, I truly don't know, if you have access to one you could *try* it.
I keep thinking maybe my kids (at 3 1/2 and 6 1/2 yrs old) are old enough now for us to get a real tank, after they broke the leetle 5 gal one I had with just a few white cloud minnows in it... but your tale makes me think I'll wait a bit longer yet
Best of luck, hope it works out for you and you can save the fish,
Pat