Misreporting a non-only child as an only child will lead to tax deviation. In the calculation of individual tax, only children enjoy certain preferential tax policies, and non-only children do not. The wrong declaration led to the taxpayer not enjoying the preferential treatment, which led to the change of individual tax calculation results. In order to ensure the accuracy of tax calculation, family information and children's information should be truthfully reported to avoid reporting errors. If the declaration is wrong, it should apply to the tax department for correction in time.