You are not allowed to do that. This is 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 parents, who are allowed to split the child benefits). The second parent should not enter the child, at all.
The mother will have to file an amended return (after she receives the refund from the first filing). She will unclaim the son's day care.
You can go ahead and file your return, but you will have to mail it in.
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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. 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, both 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.
