Where to park, or more likely, what are the public transportation options? Which public transportation stops are handi-cap accessible (and therefore stroller-accessible) - there are quite a few in Boston along popular parade routes with no elevator access. How far from the train/bus/subway to the parade route? Where are the closest restrooms? Are there likely to be food vendors or restaurants nearby or will they all be packed and/or closed? What time does the parade pass various viewing points? Around here, there can be an hour's difference between the start and end of the parade route. Do people tend to stick around (is it part of a larger event) or disburse immediately? And of course, what will the weather be?
We take our 4 kids (and usually an additional friend or two) into Boston for New Year's Eve, July 4th, and when a team wins a championship such as the World Series or Stanley Cup. We're comfortable doing this because we know the ins and outs of what T station or parking lot to use, where the out-of-the way restrooms are, whether or not it's better to stick around and eat or get out of the city first etc. but to someone who hasn't lived or worked here, I can see it being a totally overwhelming and not enjoyable experience.