Robin Williams -- Widow and Kids in Bitter Fight Over Property

Robin Williams' widow is fighting his 3 children over property the kids say is clearly theirs ... and the dispute is so bad it has ended up in court.

Susan Schneider has filed legal docs complaining someone came into the house days after Robin's death and took some of the actor's belongings. But the kids tell a very different story.

Zak, Zelda and Cody Williams claim Susan is essentially attempting a money grab by ignoring the plain language of his will and trust and trying to redefine it to benefit her.

Sources connected with the kids tell TMZ ... Susan refused to let them in the house after Robin died. We're told before Robin met Susan -- he was very clear in the trust he created ... he left his personal effects, including his Oscar for the movie "Good Will Hunting", movie memorabilia, action figures, graphic novels, theater masks and other items to his 3 children.

Susan -- who was only married to Robin for 3 years -- acknowledges she has no right to items related to his acting career, such as his suspenders from "Mork and Mindy," but she wants other items like the tux from his wedding and other "knickknacks."

Sources connected with the children say Susan can absolutely keep the items she accumulated with Robin while they were married, but they say she has gone way further. For example, they're indignant she is apparently trying to redefine the word "jewelry." We're told the kids are supposed to get all of it, but she's saying "jewelry" does not include his watch collection.

And people who were extremely close to Robin say he would be heartsick that this was not worked out between family ... privately.