Honestly, if you are committed to your marriage and child, you may need to break off interactions with your mother. That is an extreme step, but if you can't tell your mother to knock it off and treat your wife respectfully, then you owe it to your family (your marriage and your child are now your priority) to create a peaceful and loving home without the old family drama. It sounds like both of your parents border (if not cross) the abusive line.

If you want to continue seeing your parents, then yes, the best solution is to do so without your wife, but I would not do that during holidays and occasions when you should be spending your time with your wife and child. Don't expect your wife to put up with being treated abusively by your mother.

I would also suggest you tell your mother you will not listen to any complaints or negative comments about your wife, and she is not allowed to do so in front of your child. If she does, you hang up the phone or you leave. If you aren't willing to stand up to your mother and put an end to her negative comments as a show of support for your wife, what does that say about your respect for your wife?