TCM0284120 - Specialist areas - complex: change of circumstances - non-complex to complex You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals. Checklist Before you follow this guidance, make sure you are in the correct MU. Use TCM0322460 for the correct MU number. Background when an additional child joins a family that already includes 18 children when a polygamous or polyandrous marriage takes place, resulting in three adult customers in the family when a tax credits customer receiving Working Tax Credit (WTC) starts to receive income-related Employment and Support Allowance (ESA(IR))