and send it to HM Revenue & Customs.
This can either be done online or you can print the form and send it.
If you are already claiming the benefit and you have a new baby, you can call HMRC on 0300 200 3100 to add the new child to your claim.
If you do not have a birth certificate yet you will need to send this when you have it, but this won't stop your claim being processed.
New claims can take up to 12 weeks to process and the benefit can be backdated for up to three months.
It is worth £21.05 per week for a first child and £13.95 per week for additional children.
The money is for any child up to the age of 16, there's no limit to the number of children that can get the cash, and it's paid every four weeks.
If either parent earns £50,000 or more, the level of child benefit drops. If either earns £60,000 or more this falls to zero.
But even if you're not receiving the benefit, it's worth getting because you also get National Insurance credits which count towards a State Pension.
You need 30 years of contributions in order to get the full State Pension.
Financial Secretary to the Treasury, Jesse Norman, said: "We need people to stay at home in order to protect the NHS and save lives.
"Today’s change means new parents won’t miss out financially and can keep their families safe.
"The government will do whatever it takes to support people and the NHS during this outbreak, and HMRC is working around the clock to help families and businesses across the UK."
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