You could get a sump and pad lock the door to the stand, unless it's an open stand.I agree that sumps are better but thanks to my wife's cats and our youngest kid, sumps are out of the question for now. I don't know which of them are worse but I'm betting it's the kid. There isn't a child proof lock that she can't defeat and the worry is that she'll either throw something poisons to the fish in the sump or somehow knock the overflow box and cause it to lose suction.
If the stand is open, the kid could somehow disconnect a canister or try to open that up etc. I would get a HOB filter at that point.