Hi Chris,
It is probably best if you bring a laptop that your son can use at home, we have computers available to use, but then he won't have that environment at home to work on in between.
The event runs from 11 am to 1pm, we tend to start new dojo members off with an environment called Scratch, building the game Breakout. If your son already has some experience and we can see that he is too advanced for that we'll move him onto something else. We generally split into two/three groups; a group focused on games, a group focused on web development and a group of newer kids who are still getting oriented.
There is usually a led group activity that targets a middle experience level for each group and dojo mentors that are available to work one on one with kids that are not up to speed enough to participate in the group activities. If your son has his own thing that he wants to work on, he's welcome to do that as well, we'll be available to answer questions and help where needed.
There isn't really a place for kids to play in the building for non-members but there are a number of playgrounds near by or the Central Library which is relatively close by as well.
-jon