My kids don't want to come home from visits with their mom

We have 50/50 custody and I get them every other week. When I pick them up from their mom's house they're always sad and don't want to leave. She told them we're moving them around too much and that they should be with her full time. I never bad mouth her in front of them but now she's poisoning them against me. I'm furious and heartbroken at the same time. This is affecting my relationship with them and I don't know how to fix it without creating more drama. Thinking about talking to a family counselor but also wondering if I need to get the courts involved.