It's rude to uninvite them about 4 mins later because they remembered they had to go out somewhere.
My friend has done this a few times to me. She makes plans to invite us around and then stops us from going around. I find it incredibly rude, yet she is always dropping in whenever she's passing or whenever she feels like it with all her kids.
I know she has other people go around. She's good friends with my cousin too and my cousin has been around loads of times with her children. I'm paranoid it's because of my kids but they're all good kids...her youngest son breaks our toys and we've had to hide precious things when he comes...my kids don't break things.
Maybe she's just using me?