The first thing I would tell you is this. In NC it makes no difference to the court whether you even pay child support. Custody/visitation and child support are separate matters and can not be tied together.
Secondly, I suggest that you let the ex know that the children do not have a choice in the matter. It is your custodial time with them and if you have a schedule stick to it. Let her know, in writing, that your son believes that he doesn’t have to go until child support is paid up and that is not the case. Let her know that you will be there, specified day and time and that the police will be with you. Legally, she can not stop visitations due to unpaid child support. Show up an hour early if you can so they do not have a chance to leave.
Last, when you DO get your children there with you, you should sit them down first thing and talk to them about this. Show them your check stub, explain what child support is. You do not have to say their mother is lying, they will figure that out themselves, but show them that you are meeting your responsibilities and expect them to do the same. Their responsibility is to visit with you, enjoy the time they have and to be kids as long as they can. All the rest is between you and their mother. Let them know that. They should not be put in the middle of this and you are not going to put them there by discussing it. You are their father and there is nothing that will change that fact. You are doing what’s best for them. Now, when they get older, if they want to discuss facts or details, that’s entirely up to you on what you share. Until then, they have their visitations and it will make things easier on them if they just keep out of the rest of it…It sounds harsh but you have to make sure they realize that you want them there with you. You want them to know that YOU are taking care of them and that is your only concern.
If you are confronted with the children repeating things she has said about you, simply present them with the facts if you want to “defend”, tell them that they are too young for you to discuss the situation with them, or ask them if they believe whatever lie she has told. Deal with each incident as it comes up and as needed.
My husband’s ex did the same with us until both children told her they were sick of hearing about it. She even let them read the court complaint when my husband filed for custody…now at 7 & 10, they did not understand a great deal of it other than Dad was saying terrible stuff about mom. I respect her because she is their mother, but what she put them through during their divorce…I lost every bit of tolorance or compassion. She lies to them, she’s not a nice person, lets them run wild and she is a lousy mother. But they have NEVER heard me say that or even know that I believe it. They have even been with us when she yelled and screamed at me for looking at her…all I told them when they apologized for her behavior was that it was something that they didn’t need to worry about. They said but she called you a ****, and I told them, so what…that’s only a word and I know it’s not true it doesn’t hurt me. The only part that hurt me was that they heard it and they saw her acting this way.
Keep in mind that children love both parents and there’s little that the other parent can do to change that.