Most days the presidential campaign turns on insults, not white papers, but there will be policy consequences. One example is child care, with both candidates offering multiple subsidies for raising kids. This will end up raising prices and it won’t address the real reason parents feel squeezed: a decade of slow or no economic growth.

Donald Trump on Tuesday proposed a tax deduction that would let families write off the average cost of child care for up to four children, among other ideas. Hillary Clinton has already promised to limit care expenses to 10% of income; raises for caretakers; universal pre-K; an increase in the $1,000 per child tax credit; a new program for student parents, and more.

This is a reaction to the public’s sense that day-care prices are skyrocketing. Mrs. Clinton says the cost has increased 25% over the past decade, and Ivanka Trump seems to agree. Groups that favor government intervention like Child Care Aware of America roll out eyebrow-raising averages: In Massachusetts the annual cost for infant care tops $16,000, and nearly $15,000 in New York.

Yet averages are inflated by affluent parents who pay a premium for care that includes French immersion or yoga sessions. A report last year from Chris Herbst at Arizona State University found that prices “have been essentially flat for at least a decade,” and spending for low-income families hasn’t budged. The typical family’s child-care spending has risen 14% since 1990—much more modest than Mrs. Clinton and left-wing outfits claim.

Mr. Trump deserves credit for noting that regulation drives up the cost of care. States set minimums on square feet per child; licensing requirements; ratios for staff-to-children; group sizes. Zoning laws prevent care centers in convenient places such as residential neighborhoods. Regulation also limits options like informal care at grandma’s house or families who share nannies.