My son''s ex girlfriend won''t let my husband and I see our grandson.

Unfortunately based on the information you have provided, the only person with standing or legal rights to pursue custody or visitation with the child is your son, the biological father.  Grandparent visitation is very limited in the state of MI and you would not qualify under the statute.  Your ability to see your grandson will depend on your son pursuing his right to custody and parenting time.  This response is general in nature and is not legal advice.  I urge you to have your son consult with an attorney as soon as possible.  Good luck to you and your son.   Patricia A Kasody-Coyle Esq.