I now it’s a bit hippy but I think a lot of people get bogged down with tasks and almost forget to enjoy their children’s nd have fun with them and it’s easy to forget and to notice all the good things they do
I think this is rubbish if you're talking about reasons for children to behave badly. It may well be true at times, and certainly as a parent who has suffered the loss of a child I am sure you're more attuned to this than most of us because you are so very conscious of the moments you've lost. I'm deeply sorry you have had to go through that.
However, I think it's too simplistic to say that badly behaved children are the result of parents who don't have good relationships with their children. Many parents have great relationships with their children, but don't perhaps have the skills needed to parent that particular child the way he/she needs. Others may have less good relationships but nonetheless meet their child's needs. Similarly, there are a lot of other factors at play from the child's natural personality to environment, school, other influencers etc.
I DO believe that parents with a very bad relationship with their children or who are unable/unwilling to engage with them at an appropriate level are likely to set their children up for a more difficult life and behaviour issues. But it's not guaranteed (because it's more complex) and there's definitely no one thing that leads to difficult children.
I also am not sure about how important "well behaved" is. That's just one element of a child's personality and upbringing. My children are broadly speaking, very well behaved. However, they have other challenges which DH and I have to manage. And as they've got older, those challenges get help from other quarters too - school, other role models etc. If I chose to define how "good" my children are purely by behaviour, I'd likely be happy to ignore the other things. As a responsible and loving parent, I'm equally focused on those things and want to help my children overcome all challenges.