How do I stop my friend from asking to come over?

I've been friends with her for over 14years and I have no issue with her visiting, the issue I have is that she brings her 2 children aged 10 and 6, who she claims are mis-behaved due to their autism, but I think she is slack with her parenting too. I find myself making all kinds of excuses to prevent her coming over with her kids , mainly because they are loud and naughty but also because her 6 year old girl poops herself so anything she sits on is tainted with the smell of poo. I have 3 kids myself so have no issues with kids, just hers. Recently she has asked everyday to come over and im just not in the mood to be cleaning my sofas everytime they leave! I offer to go there and last min she says no we will come to you and I have no excuse , how do I stop her asking all the time, or should I just be honest? I Feel bad telling her the real reason!
How do I stop my friend from asking to come over?
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