If the divorce decree clearly states that parent A will have the child on that specific date and time but parent B refuses to hand over the child then parent B can be placed under arrest. How much force is justified? Depends on the situation, just like with any arrest. The force would be the same as if a child was deemed in danger and authorities needed to take the child from the parent. Is parent B just running late because they are stuck in traffic? Probably no arrest. Is person B standing there saying "F*&^ the judge, I am not giving up my child"? they are more likely toy be placed under arrest. My understanding is that it quite rarely comes to that level though, no cop wants to yank a child out of a parent's hands. Most situations can be resolved by calm talking.
Of course different jurisdictions may have specific laws which may change how these things are handled so I am making a general statement, not a universal one.
I was unaware that the police or sheriff had the duty to enforce family court orders without a specific warrant to be executed.
My understanding is that calling 911 will get a police report filed, and they may try to talk to the party violating the visitation schedule. Beyond that, unless the child is in danger or the uncooperative parent's conduct rises to the level of being criminal, the Cops are most likely going to tell you to go to family court and have a judge sort it out.
The judge can issue a warrant for the parent's arrest (criminal contempt of court?), issue a court order demanding the child be turned over to the other parent, etc. But the Cops are unlikely to be the enforcer of a visitation agreement. This is not a CRIMINAL court case -- it's family court. Just like Cops don't get involved in civil law matters unless a crime is committed.
i'm not a lawyer, but I've seen how these courts function. They have distinct and separate areas of law, and the Cops are only part of the criminal justice side.
Sheriff deputies would most likely be the ones to execute a family court order anyway, just like they handle evictions and other civil matters.