Jarts were a brand of lawn dart toy first sold around 1950 per some sources, or 1940s per others. You would toss them, trying to land inside a circular target. They had a weighted metal tip so they would stick upright into a lawn.
This was not a very good idea.
The metal tip was heavy and could fall with enough energy to penetrate a skull. At least three children were killed, with many thousands of injuries from mild to severe. Over 6100 in the US alone were sent to emergency rooms.
Attempts to ban the toy started around 1969. The US took them off the market in 1987, and Canada in 1988.
Similar toys are sold today, minus the deadly weapon part, with nerf or blunt tips designed to avoid penetration injuries.
Here are some actual jarts.
The green package is clearly a later variant, and it's interesting the tagline has changed from "An outdoor game for the family" to "An outdoor skill game for adults"
I can only assume at that point they were well aware of the danger and figured they could swerve some of the legal liability if they branded the game as adults-only (despite also knowing most of the time it was kids playing)