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Kylie Jenner and Travis Scott have separated -- either temporarily or permanently -- but they don't see the need for a child custody agreement, and that follows a long tradition in the Kardashian clan.

Sources with direct knowledge tell us, none of the sisters have ever put pen to paper to set the ground rules for custody. Our sources say Khloe and Tristan don't have a written custody agreement regarding True, and Kourtney and Scott also don't have anything in writing -- mind you, they have 3 kids.

When relationships hit the rocks and kids are involved, it's typical for parents to run to their lawyers and to court with a very specific custody arrangement -- how much physical and legal custody does each parent get, who gets the kid(s) for various holidays, who pays child support, etc. There are no such agreements with Kylie, Khloe and Kourtney.

Rob's a different story. His relationship with Blac Chyna was contentious and even allegedly physical, so it's not surprising he and Chyna memorialized the arrangement for Dream. It is interesting, however, because both Khloe and Kourtney had significant issues with their baby daddies at the time they split, but still, they didn't commit their custody arrangement to writing.