Both parents are catholic. One wants to baptise their 2 month daughter and the other does not. He feels the child should make its own choice when she is older. He was baptised into the catholic faith just before marring my daughter.
I’m not sure I’d say such a parent is guilty of a mortal sin since they may be acting out of ignorance. That being said, they are being negligent in their canonical duties as a Catholic;
Can. 867 §1. Parents are obliged to take care that infants are baptized in the first few weeks; as soon as possible after the birth or even before it, they are to go to the pastor to request the sacrament for their child and to be prepared properly for it.