Reoffending Nightmare - From Corrine

Dear PFV. I am a fan of your site and hope you can help in some way. My children's Dad keeps on reoffending and it is having a profound impact on them. They love their Dad and although he and I are no longer in a relationship, I have kept to my side of the bargain and take the children to visit him in prison. But he is only out for a few weeks/months and he is back inside again! I can't handle seeing my kids upset every time I take them to see him in prison, it's not fair on them.
Maybe I should stop taking them but then is that fair? Thanks in advance.