Children's Interest

I currently keep my children's savings in an account in my name. The money has been gifted by their grandparents over the last 9 years, of which we have records. In order to use the £100 tax relief on interest, can the savings be kept in my account, or do they need to be in a specific child's account in their name? I find it easier to transfer the savings to the best interest rates doing it this way, as the children's accounts often need a visit to a branch. Also, can the cumulative interest earned over the last 9 years be disregarded, and only the interest earned from this year's contributions into their account (be it theirs or mine) be declared? Or is the £100 relief applicable to the total interest earned over the FY, even though it's from previous year's contributions?

Hi,
They would need to be in childrens accounts - Interest on savings for children
Thank you.