You know, anything is possible. I doubt it's related though. It
is irresponsible having your tank where a little kid an reach it though. Water weighs a bit over 62 lbs/ cubic ft. I don't know how big your tank is but it's definately a hazard if he pulls it over on himself, consider the weight, broken glass, etc... Definately a DOA possibility.
As for him throwing up being related to playing with the tank, I still doubt it's from palytoxin, however recently, a local, very experienced reefer in the CORA forum had a severe life threatening infection after fragging some zoas. The way I understand there were three different marine organisms isolated in his bloodstream, so there is some danger. Have a look at this, it's first hand, recent, directly verifiable info, not washed through the internet "grapevine".
http://www.reefcentral.com/forums/showthread.php?t=1838538
Tim