[Zope] How do I count children?

So In ZUBB (my discussion product) I want to be able to show how many replies there have been to any one main topic. All replies are 'children' of the main post and when I state it with <dtml-tree branches=children> Stuff </dtml-tree> It works and knows that each message is a child of the message. When in go through a searchResult to list the message I want to show many replies there are to that message. Q: How do I count the 'children' of any one onject? Thanks, J