Family issue

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So I been having problems with my childs father because his family dont come see his son he got mad that I didnt let his mom take my son after she called saying she should be allowed to take him when she wants because it's her grandson and it's not right my mother sees him mind you I dont drive or have a car and she lives about 15 mintues away from me and only seen him twice and hes 4 months old am I wrong for telling her she cant take him until she gets to know him and how he likes certain things?