(WPXI) – The Internal Revenue Service, which will begin to process income tax returns Monday, is urging taxpayers to make sure they have accurate information as they file their 2021 returns. Taxpayers should have received at least one of two letters from the IRS that they will need to file their return. If they have not, they soon will, the agency said late last week. The letters, one concerning the Child Tax Credit and the other one concerning stimulus payments, will be needed for anyone filing a 2021 return. The first letter, called the Advance CTC letter 6419, was first sent out in late December and is still going out to those who receive the credit, the agency said. The second letter concerns the stimulus check sent out last spring and the third Economic Impact Payment letter 6475 should be getting to taxpayers in late January.