There is not a per se law that prohibits them from sharing a bed.  However, it is preferable that they do not share a bed for multiple reasons.  First, it does raise concerns about his ability to provide for his child if she does not have her own sleeping accommodations during visits.  Second, it could also raise concerns that more is going on, (i.e. sexual abuse) because a grown man does not need to share a bed with a minor girl.  Because of these issues, many judges will impose restrictions in custody orders which provide that the child will have his/her own sleeping accommodations.  If this is a concern of yours (and it probably should be), you can file a motion to modify the parenting plan such that he is required to arrange for a separate bed for the child.  If this type of restriction is already in your orders, then you should file a motion to enforce.