SAIM2430 - Interest: taxation of interest: children's accounts
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Accounts held by unmarried minor children
Interest arising on an account held by an unmarried person under 18 is treated as income of his or her parent if
- the money in the account was a gift from the parent, and
- the interest exceeds £100.
The gift constitutes a settlement and ITTOIA05/S629 (1) applies to treat the interest as income of the settlor. There is more detailed guidance, with examples, at TSEM4310.