Yes, but "free" and "universal" are two different things. There are not seats for every kid at 3 & 4 years old (by state law there must be one for all 5 year olds). It's luck of the draw whether your kid gets one or not. In fact, most seats for 3 year olds go to kids with identified learning disabilities and if you don't have an older sibling already in a school to get preference the odds get kind of long to get in. They've been expanding access, but it needs to be universal.

Washington, DC had much worse schools than Boston not too long ago but they are ahead of us on universal pre-K and it's demonstrating that the results are worth the investment.