My mum was the hands on parent, and I think she was just not very good at assessing risk or at being assertive in situations where she did perceive a risk. Some examples:
Was allowed to play with things like knives, fire, electric drills etc unsupervised from the age of maybe 9 or 10.
They once left me and my sister alone all evening when I was 8 and my sister was 3 (dinner party at their friends' house).
I was allowed to continue playing with my Scalextric after the back came off the plug, even though I occasionally got quite nasty electric shocks.
Various other things too, but that gives you an idea.
They now occasionally babysit for my 3yo DS, and have had him overnight a couple of times. The problem is that even though my mum dotes on him, I can't stop worrying that she will put him in danger without realising. I know it has happened at least once when they let him play alongside the edge of a lake by himself when he was 18m. They realised it was dangerous afterwards when they saw the look on my face and have not done it since... but I can't anticipate everything and point out the dangers to them ahead of time.
There is also a separate issue with my Dad being emotionally abusive towards me when I was a teenager; things like abusive/derogatory language, unpredictable rages, and quite controlling behaviour. I think this is less of a risk as he has mellowed now and I always ask my mum not to leave DS alone with him. However, it is another big worry.
How have others handled situations like this? Am I being unwise to let them babysit, or am I overreacting?