You can put on any boundaries you want for yourself. If your ex acts like a baby in response, it is not your fault.
I have the opposite happening, ex refuses to enter the house. He asked for me back, I said no. He asked for me to stop claiming child maintenance, I said no. He said our dc can't go to my mom house, I said no.
He threw a tantrum and stopped answering our eldest son phone and calls. And then went cold turkey for 6 months. Since dc are humans, with human emotions they missed him and cried for him.
I 100% know, that it was/ is ex decision to abandon his own children. Like it is your ex decision to abandon his own children.
All you can do is to comfort your dc and give them stability over what you can. You can't force a grown man to do the right thing.
My ex came last week, dc are children so they were happy to see their father. Ex refused to stand near my house when he arrived. I assume he came back because child maintenance caught him working and sent me a letter saying he need to back pay me.
I allowed ex to take the dc, because I wanted them to see with their own eyes, it is not me that is preventing them from having a relationship with their father, but this is actually an active decision he himself made.
Ds1 said "dad was moving house that is why he wasn't able to see us and I decided to believe him." Even ds1 knows ex is talking nonsense, I just responded to ds1. "I know you love your dad very much, never forget I love you very much".
I have every right to:
1.claim child maintenance
- refuse to take ex back
- Take my dc to see my mother who has no safeguarding risks. (Ex just hate how much she and my family help me.)
Maybe repeat factual information to yourself. You have every right to refuse your ex entery to your house. You not preventing him from seeing the dc. Ex is actively choosing not to see his own children. This is not your fault. Ex is an adult who, made the decisions that are morally wrong. You can't force an adult to do the right thing.