Couples could be asked a series of personal questions as part of the Government's move to axe child benefit for high earners.
The coalition's decision to means-test entitlement might lead to intrusive inquiries from tax officials as they tackle recipients they believe over-claim.
Parents may have to declare their family circumstances alongside their earnings to determine whether they can claim the benefit, worth £20.30 a week for the first child and £13.40 for each subsequent child.
The benefit will be paid to couples unless they have opted out of receiving the money, though households where one parent earns more than £60,000 will have to return the entire amount through the self-assessment system.
The benefit will be reduced on a sliding scale for households where mothers or fathers earn between £50,000 and £60,000.
Families could be quizzed on the volatility of their relationship, whether they have a history of splits, who pays household bills and who funds children's pocket money, if anomalies are identified when self-assessment forms are returned, the Sunday Times reported.
They will be told not to ask any questions about sexual relationships, although they "should take note of any information volunteered".
But HM Revenue and Customs (HMRC) stressed households completing the forms honestly and accurately would not face questions.
A spokesman said: "HMRC believes the majority of its customers want to comply and we will be putting our efforts, in the first instance, into supporting them to do so.
"However, for those who choose not to play by the rules, we will use our standard compliance risk-based approach to tackling non-compliance, where appropriate.
"Nobody affected by the new charge needs to complete a tax return until January 2014, so HMRC will only contact people after that date, if further information is required.
"Nobody should worry about a call from HMRC where they have correctly told us about their circumstances."