Cancelling a children's isa due to change in circumstances

xylophone

No, it could well be the child's actual mother who opened the account.

Certainly a possibility but as it appears to be the father who is attempting to close the account, I'd guess he is the registered contact?

https://www.gov.uk/junior-individual-savings-accounts/manage-an-account

Manage an account
Your child’s Junior ISA will be in their name, but the parent who opens it is responsible for managing the account and is known as the ‘registered contact’.

The registered contact is the only person who can:

change the account, for example from a cash to a stocks and shares Junior ISA
change the account provider
report changes of circumstances, for example change of address