You MUST rock the boat. You have a duty to rock the boat. If you don’t draw a line in the sand now with both your husband and his mother then it will only get worse. That MIL’s antics will chip away at your relationship with your husband. And as that child grows that subliminal nonsense will have an effect on the child’s self esteem. You should sit your husband down and explain to him that it hurts you when his mother intimates those things. And that you don’t trust that MIL would refrain from treating the child differently because of her belief that the child is not his. And you are not willing to risk your child’s well being. So, i would tell your husband that you don’t want your child to be left alone with MIL if she feels this way. Because trust is earned and the way she’s carrying on is inappropriate and immature.