Ugh! How awful! Don't panic...if it is a flea and not bed bugs, it probably won't lead to any kind of infestation in your house. I wouldn' tell the other parents at this point...I mean you only found one flea on the child...not on anyone else's kids. They might panic for no good reason. I don't think fleas usually travel around on people...as far as I know...so I like Kidlove's suggestion of treating your pets with an extra flea bath just in case. And vaccuum everything really really well...especially the crackes where eggs could fall into (like near walls). Again though, it was one flea...I wouldn't panic at this point. And I think I would ask that the child not return until their pets and home have been treated. I don't know what kind of proof you will ask for...maybe reciepts for the products used? Good luck! Ick!