20 CFR §10.417

1. (a)Compensation payable on behalf of a child, brother, sister, or grandchild, which would otherwise end when the person reaches 18 years of age, shall be continued if and for so long as he or she is not married and is either a student as defined in 5 U.S.C. 8101(17), or physically or mentally incapable of self-support.
2. (b)At least once each year, OWCP will ask a beneficiary receiving compensation based on the student status of a dependent to provide proof of continuing entitlement to such compensation, including certification of school enrollment. The beneficiary is required to report any changes to student status in the interim.
3. (c)Likewise, at least once each year unless otherwise provided in paragraph (d) of this section, OWCP will ask a beneficiary or legal guardian receiving compensation based on a dependent's physical or mental inability to support himself or herself to submit a medical report verifying that the dependent's medical condition persists and that it continues to preclude self-support. If there is a change in that condition, the beneficiary or legal guardian is required to immediately report that change to OWCP.
4. (d)In the case of a dependent incapable of self support due to that dependent's physical or mental disability where the status of that dependent is unlikely to change, a beneficiary or legal guardian may establish the permanency of that condition by submitting a well rationalized medical report which describes that condition and the ongoing prognosis of that condition. If the permanency of that condition is established by such a report, OWCP will not seek further information regarding that condition; however, if there is a change in that condition, the beneficiary or legal guardian is required to immediately report that change to OWCP.