You make one Child Benefit claim and include both children, rather than submitting a separate claim for each child. Only one person can receive Child Benefit for each child, so parents should agree who claims; the claimant may also receive National Insurance credits towards State Pension. The amount for the eldest child is usually higher than for additional children, and the High Income Child Benefit Charge may apply where an adjusted net income is above the relevant threshold. Check the latest rules and apply through the official GOV.UK Child Benefit page.