The rules come from the Childcare Act 2006 and the Childcare Disqualification Regulations 2018. KCSIE 2026 says they are in addition to the usual DBS checks (paragraph 342). They mainly apply to staff working with children aged 5 and under, including reception classes, and also to wraparound care for children up to age 8, such as breakfast clubs and after-school care, and to anyone directly concerned with managing that provision (paragraphs 343 to 345).
A teacher working only with, say, year 5 during the school day is not covered, so one form for every member of staff may not fit.
Who it doesn't cover any more. Disqualification "by association", because of who someone lives with, no longer applies in schools. It only applies where childcare is provided in a domestic setting, and schools are not entitled to ask staff about the cautions or convictions of people they live with. This is set out in the DfE's statutory guidance Disqualification under the Childcare Act 2006.
That guidance also says a self-declaration form isn't required. Schools should keep a record of the staff who work in or manage relevant childcare and the date they gave the information, either on the single central record or separately. A disqualified person can only work in that provision if Ofsted grants a waiver for the role.