Ex speaks down about me to kids

My ex fiancé has finally made the step to be a better father to our 2 kids and for the first time in 2 years he took them for a sleepover and has promised to be consistent in their lives. I’m new to this as it’s been just me since I broke things off with him. I’m so happy for my kids sake and I love he wants to be more involved, but there’s been a few things my kids have told me about the way he talks about me in front of him and the things he says. How do I deal with this? Do I ignore it and not make a big deal out of it? If I was to say something to him about it it might turn into an argument by him and I know it isn’t worth it, but at the same time I don’t appreciate him speaking of me that way in front of our kids and his current girlfriend. He knows for a fact our kids would come back and tell me, as they love their mama and dislike anyone speaking down on me.