Here's the thing, OP. Your kids are their own independent people and not an extension of you. To some extent, they have to take responsibility for their own lives and outcomes.
They could have done incredibly well without any pushing from you - many kids do. And it isn't necessarily your fault if they chose not to push themselves.
Also, you have no means of knowing how things would have turned out if you had been pushier. You can't possibly know what that might have done to your relationship with your kids, their mental health etc.
It can be hard to work out where parental responsibility starts and stops and where individual responsibility kicks in. But there is no point in beating yourself up about stuff that you can no longer change.
If your kids want to turn things around for themselves, they will have that opportunity. But if they're old enough for you to be able to feel this level of regret, I'm guessing that they're at an age now where it is mainly up to them.
It's easy to say that you would do things differently with hindsight, but the reality is, you never get to see how that would have worked out in any case. If you made what you thought were the best decisions at the time, that's all you could have done. No point in wasting your energy on empty regrets. Channel that energy into supporting your kids as well as you can in the present instead, whatever stage of life they're now at.