It’s always tempting to make promises in a State of the City address — especially in an election year.

And Mayor Marty Walsh had more than a few in his message last Tuesday. High on his list was this:

“I will file legislation to finally eliminate the opportunity gap in early education, and for the first time in Boston’s history, offer free, high-quality pre-kindergarten to every single 4-year-old in our city.”

And if the job of mayor came equipped with a magic wand, we have no doubt he’d do just that. The goal of giving the city’s children a leg up on education is certainly an admirable one.

But there is no magic wand at City Hall, and the legislation and the funding source the mayor is proposing to use are one heavy lift.

Walsh wants to tap two tourism funds that are currently directed into a larger Convention Center Fund. The surcharges on car rentals and sightseeing operations in the city amount to $16.5 million a year, city officials calculate.

“Neither revenue source is directly related to convention center business,” a statement put out by Walsh’s office contended. “Boston residents have a strong claim on this revenue.”

Well, yes and no.

Those cars and buses and Duck Boats do clog the streets of Boston, even if those revenues come from the tourists who help this city thrive with their presence and their business.

And the funds, which were originally intended to help finance an expansion of the Boston Convention & Exhibition Center, now mercifully put on hold by Gov. Charlie Baker, do constitute a “surplus.” There have, of course, been far more profligate uses of what amounted to a Convention Center slush fund under its previous administration. Funding the worldwide travels of Gov. Deval Patrick and his team come immediately to mind.

But right now the two surcharges in question are part of a larger pool of money that has been used to simply balance the state budget — at least as a stopgap measure. So it seems unlikely state lawmakers are going to be falling all over each other to hand over a pool of revenue for the exclusive benefit of its capital city.

Walsh deserves points for creativity perhaps, but statewide needs deserve a statewide solution.