> I think if you're breaking even on daycare and salary then you're still coming out economically ahead to keep working.

That's the traditional wisdom, with the assumption that consecutive working years will result in a more lucrative career, which balances the child care costs on the long run.

That assumption breaks depending on how much you pay for day care (including meals, potentially an additional baby sitter etc) and how much you expect your career to last in that company, or if your skills don't devaluate so much you can get back to work some other place after a few years.

For more and more people, a 3-4+ years career gap isn't that big of a deal, "I raised my kid" is a fully accepted explaination, and their company won't value their continuous work that much either.