Bare Trust holding Property Registration

I am one of the four trustees for a Bare Trust with my 7 month old Granddaughter being the beneficiary. The Trust holds a rental property generating around £15k p.a. income. This Tax year the income will be below the current Tax Free Allowance. I have already registered the Trust & Trustee details with HMRC. Do the property details now need to be entered immediately, and if so, where, or can they be declared when completing an SA100? Income Tax will not be due until 2025/6 at the earliest, so do I complete an SA100 for my Granddaughter after April 5th 2025 or after April 5th 2026. Comprehensive digital income/expenses accounts will be maintained along with records of all the Trustees decisions on mamaging the Trust.

Hi,
A bare or simple trust is one in which each beneficiary has an immediate and absolute title to both capital and income. The beneficiary of a bare trust is taxable on the trust income and gains. Beneficiaries must include trust income and gains in any tax return they are required to complete or in any forms R40.
You can see guidance here:
Trusts and taxes
Where a Self Assessment tax return is required, the trust income is declared on supplementary page SA107. Please note that to submit an online return with a SA107, will require that you purchase a commercial tax return. HMRC online return cannot be used. A list of commerical returns can be found here:
Self Assessment commercial software suppliers.  
The alternative is to submit a paper tax return, which can be downloaded here:
Self Assessment tax return forms 
Thank you.