HMRC says a new Child Benefit claim can take up to 12 weeks to process, although the time may vary. You can generally claim if you are responsible for a child under 16, or under 20 if they remain in approved education or training, with the final decision based on your circumstances. If approved, Child Benefit can usually be backdated for up to three months, so claiming promptly may help. Check the latest guidance and processing times on GOV.UK.