Hi Netra,
You set the age eligibility limits for health plans in table V_74HT_D (SPRO --> Personnel Management --> Benefits --> Flexible Administration --> Dependent/Beneficiary Eligibility --> Define Dependent Eligibility Rules). If the maximum age is set to 26 for children, they will be greyed out and cannot be included in the selection for individuals to be covered by the health plan in HRBEN0001. If they were previously eligible, say age 25, when they turn 26, running the Participation Monitor (HRBEN0003) will identify them and allow you to stop participation.
Try this to satisfy your requirements.
Paul