@Hani92
The amending deadline is three years from the original deadline for returns filed on time (so April15, 2022 for a 2018 return filed on or before April 15, 2019) but two years after the date of filing for a return filed late.
I don’t know how he would prove where the children actually physically lived in December 2018. That’s his problem. The IRS is unlikely to award him the dependents and take them away from the other parent unless he has better proof than she does that the children lived with him for more days after the separation than they lived with her.
