If they do it like they do here, they will have a certain position group (or 2) signing that day.  They set up a couple tables and there are a couple lines.  What players sit at the table for your line is a crap shoot.  And it's for kids...  not adults.  They only let kids get autographs.  Since my son is under 7, I get to walk through the line with him.  You'll probably have to do it with your grand-daughter or have your son do it.  Again, not sure how they will do it in Oxnard, but that's how it goes here.  You might get lucky and catch a few by the fence after or before practice...