Katherine Jackson -- TJ Deserves $9k per Month to Care for MJ's Kids

TJ Jackson deserves $9,000 per month to care for Michael Jackson's 3 kids ... this according to MJ's mother Katherine Jackson.

Katherine just filed legal docs ... asking the court to sign off on her request to have the Michael Jackson Estate pay her grandson TJ for his care-giving duties for Paris, Blanket and Prince.

In the docs, Katherine says she originally suggested to TJ that he be paid more than $9k per month, but TJ rejected the deal ... saying it was simply too much money.

In the docs, filed yesterday in L.A. County Superior Court, Katherine claims TJ eventually agreed to $9k -- $108,000 per year -- which is roughly equivalent to the salary earned by the children's full-time nanny.

Katherine says the salary is justified because he spends an average of 300 hours per month caring for the kids -- taking them to various appointments, extracurricular activities (karate, athletics, guitar lessons) and social outings.

Katherine says TJ -- Tito's 34-year-old son -- also helps the kids with their schoolwork and attends all school functions, including back-to-school nights and parent-teacher conferences.