I have a small child, and sometimes I have to pass the kid off to my wife so I can view a clinic. At times, her times run over, or there are issues with diapers, or otherwise. Since I'm taking personal days to even be at this convention (thanks, large district), I have no qualms about bringing the kiddo. Unfortunately, baby time means I am occasionally late.
As for leaving early - there are times when the name of the session has virtually nothing to do with what the person is actually talking about. Presenters need to be more specific about what their presentation is about, and then actually STICK TO what they say they're going to present. Using a 60 minute "build a better program through fundamentals" session to pitch your latest and greatest technological doodad or wunderprogram is not what I want to see at a TMEA session - especially if they don't say that they're going to do so in the session notes! Give me practical knowledge that I can use.
When that happens, I leave, and I make no qualms about it. If I get into a session where I'm sitting on the floor/standing against the wall because I get there late, and I've already heard that session before (at TBA, or a year ago, for example) then I'm also likely to head out.