Signs of rust in Engine any Ideas

Just a question do you have kids, this happened to me before my business partners son about 7 at the time decided to help us clean a customers GSXR750 he stuck the water hose up the exhaust and filled the engine slap full of water, when we asked him why he did it just said he was cleaning the inside of the pipe cause it looked dirty. We got lucky and caught it cause someone saw him pulling the hose out of the pipe no damage but still cost us alot of money to tear down and inspect and replace all the gaskets. So sometimes Sh.....T happens and you don't even know.