[flexcoders] Add items to an array list as a child

[timgerr]

Hello all, 
I have a question for you all.  I was wondering how I can add a child to an 
object within a arraycollection.  Here is what I mean:
var myCollection:ArrayCollection = new ArrayCollection([{first: 'Matt', last: 
'Matthews'}, {first: 'Tom', last: 'Jones'}]);

var obj:Object = new Object();
obj.first = 'lisa';
obj.last = 'griffen';

I would like to add the new object to be a child of the first item in the array 
list.  Can this be done??

Thanks,
timgerr