“In our custody papers, my ex has now received every other week during the summer. My children are refusing to go with him. We live in California. My children are 14 and 11. He says he is going to make them and if he has to call the police to make them he will. My son is 14 and my daughter is 11, if they refuse to go with him, I am not going to physically make them. My question is, can he physically make them go? Can the police physically make them go and if they don’t go will I be in trouble?”
If your ex shows up with a valid court order, and you are not cooperating with effecting the order, then yes, your ex will be within his right to ask the police to enforce the order, and the police will do so.
More to the point, why are you not supporting your ex’ relationship with your children? It seems from your question that your children’s father has requested time with his children, and the court has granted it. Why are you not supporting his relationship with the children? They are his children too. Children of 14 and 11 – particularly those of 11 – rarely turn on a parent without some coaching (intentional or otherwise) from the other parent. This is known as “parental alienation”, and is grounds for a change of custody in California, and other states.