Apparently HMRC did on your child's behalf?
www.gov.uk/government/news/thousands-of-teenagers-missing-out-on-child-trust-fund-cash
CTFs were set up for all children born between 1 September 2002 and 2 January 2011 with a live Child Benefit claim. Parents or guardians set up these accounts with Child Trust Fund Providers – usually banks, building societies or investment managers – using vouchers provided by the government. If an account was not opened by the child’s parent, HMRC set one up on the child’s behalf.
I didn't realise this, and I've felt guilty for not setting it up, as well as a new baby had a lot else going on at the time!
I've now filled in the form to see if indeed there is one. Will post back with the news either way.
(And perhaps have the hassle of making it fair for DC who was born after the cut off!)