When I’m in the room with them, the barricade is sufficient to keep them in the room, as long as nothing too interesting is happening in the hall. Then they can play Door. It’s got enough gap at the bottom to fit a paw partway through. They have yet to discover the hinge-side gap, but this has been good. They enjoy the mystery of poking at each other when they can’t see each other.
I also have to keep our own cats out. When Snuggles heard me open a new bag of kibble, she hopped in. Then everyone stood around stiffly. Pam gets quite a ridge on her back when she’s scared and trying to look tough. Snuggles didn’t really want to be with the kittens, and she knew the kibble wasn’t hers, so she left pretty quickly.