If you and the other parent live together, either one of you (but not both) may claim the child. You may decide between you which one will claim the child. Or you can each claim one child. Only if you can’t agree, do the IRS tie breaker rules apply, to see who has first choice. It may be worthwhile to prepare trial returns, three ways, to see which way the family comes out best. This tool may be useful: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
A common error is when unmarried parents live together, If you and the other parent live together, only one of you can claim the child for any tax benefit. The interview is confusing (it's designed for divorced and separated parents, who are allowed to split the child). The second parent should not enter the child, at all.
