How much antifreeze is fatal?

I actually looked up this question becauses of all the true crime movies I watch, like Stacey Castor movie ... I do know that someone I grew up with lost her younger brother I believe he was around 4. Apparently the "dad" was doing work on his car and their son drank water out of a puddle in the driveway - he passed away so for a 4 year old it was exceptionally limited so after the web sites I have veiwed including this one - it is a very scary thought and maybe that should be a new invention is something less toxic and antifreeze should be banned.