Charlie Chaplin accomplished many things in his career as an actor, writer, musician and producer. There is not any greater morality tied to stardom in the 1920s then there is today, so why should it be unsettling or impossible to consider that Mr. Chaplin may have enjoyed himself either between or outside of marriage?
Given that he had multiple affairs, multiple marriages and fathered at least eight, and maybe twelve children, it's certainly possible he had a "love child". Chaplin had an affair with Joan Barry who named him as the father of her child in a paternity suit. Chaplin was ruled to be the child's father. Sometimes rumors are just rumors, but sometimes there is a kernel of truth behind them.
Charlie Chaplin's biographers have pointed out that the actor himself bragged about his promiscuity. Chaplin claimed to have had numerous sexual partners over the course of his life. This makes it plausible that he had a child with a 1920s starlet, and that the affair and child were kept secret.
This is the first I have heard of this, and I really like Charlie Chaplin, so I think that means there is not much proof that he fathered a secret "love child." In today's technology, we could administer a DNA test, and I haven't heard of that happening, so I don't think it is true.