Sadly, you can’t turn the clock back and behave differently. It sounds like you were eager to be seen as ‘supportive’ of your kids, but failed to see the harm you were causing. Kids need to learn to weigh the good against the bad in all aspects of life. It was wrong to expect their dad to be ‘perfect.’
If you are to have any hope of fixing their relationship with their father, you’ll have to be honest with them. Tell them how bad you feel for throwing their dad under the bus. List the many ways their dad was a good dad. Show them this article and the hundreds of comments so they can read the stories of kids who hate their dads for a good reason. With a bit of perspective, I’m hoping they’ll have a better understanding of how things really were in your home, and apologize to their father if they believe it is appropriate. Your husband deserves credit for things he did right.