I regret nothing, even bad things that happened were lessons. And without those lessons, good and bad I would not be where I am now. Of course if I was in a bad place now perhaps I would have regrets.
There are things I wish I did, but if I had done them my life may have been very different. I think once you have children it is hard to regret anything because that would have changed who they were entirely, either by having a different partner or a different egg/sperm.
The one thing I am glad I did was travel and work around the world for 3 years. I learnt more about life during that time than any other education or work could have given me.