The dad has temp physical custody and mom was suppose to let her have them every other weekend but has not. He got arrested for meth and child endangerment and they took the newborn baby away. His girlfriend was at work. The other two kids (my grandkids) were at his moms house and now they are hiding the kids from the mom. Police say that he let the his mom have the kids and it's a civil matter they won't do anything, how does my daughter get her 2 kids back from his mom my daughter is their mother. L is 3 almost 4 and n is 2 almost 3.

Family Law
Children all of these thank you cyndie
Criminal Law
Missing Persons

You daughter hires a family law attorney and fights for sole legal and physical custody.

Just an FYI, it is never a good idea to place the names of the children on an international website.

Does she have court ordered physical custody? If so then the police must be involved as it turns to a criminal matter if the children are being hidden and kept away from a parent during their court awarded time.

... Police say that ...it's a civil matter they won't do anything, ...

Unless a crime is being committed, or the police are specifically ordered by the court to do something it is indeed not a police concern. She needs to get the judge to order the person, who is keeping the children in violation of the custody decree, to show cause why he or she should not be held in contempt of court. If the judge finds that person is in contempt, he or she can be put in jail.

It is unclear who that person is. As near as I can decrypt the OP's post, OP is the maternal grandmother, and the person who has the children is the paternal grandmother (the mother of the children's father). If she is not a party to the custody case, OP's daughter (the children's mother) needs to file suit against her.