HMRC says a new Child Benefit claim can take up to 12 weeks to process, although the time may vary if it needs to check your information. You should receive a letter confirming the decision and payment details once your claim has been dealt with. If you have heard nothing after 12 weeks, contact the Child Benefit Office using the details on GOV.UK. Child Benefit can usually be backdated by up to three months, subject to meeting the relevant conditions.