I think if you look at it as "everything is a calculated risk," you'd find that the only way you'd rationally consider this any riskier that various other things they could have chosen for their weekend activity (such as a road trip) was through the 20-20 hindsight that is conveniently available to you.

Since we don't even know how what caused their deaths, it's quite premature to blame the parents for doing something risky.