My question involves name change laws in the State of: California

My ex husband used to live in kansas, I have no idea where he is now or care. He has never supported the kids or sent child support. He doesnt call , visit, or care but he previously refused to relinquish his rights as to hold me hostage. My husband has been my childrens father and daddy for 4 years. They use his last name as an alias at school and church. They want to make it legal and so do I. Can I do this without the absents parent consent? At what age does the court recognize the minor old enough to request this on their own?