If your child was born between 1 September 2002 and 2 January 2011, a Child Trust Fund would have been opened for them and the government will have added money to it.
Once your child reaches 18, if they have mental capacity they can access the money themselves. As a parent or guardian you can’t automatically access any bank account for your child, including their Child Trust Fund or Junior ISA, even if they’re disabled or don’t have mental capacity.
If your child has fluctuating mental capacity, once they are 18 they can set up a lasting power of attorney for property and financial affairs which would let you manage their accounts.
But if they don’t have mental capacity you would need to apply to the courts as described in the section above in this guide. If you do this before your child turns 18 you won’t need to pay the normal fees. Remember that this process can take several months.