Can't resolve user in child domain

Hi,

I have a parent domain and 2 child domains. In my parent domain, I've installed TFS 2012 (although this is not about the software itself, but rather a resolution issue with AD). When I attempt to add a user on the child domain, which can be chosen from the location box, no entered user (e.g. Administrator) resolves to an AD object (i.e. get the message saying could not be found).

If I am trying to find a user in a child domain, is there any special AD or DNS setup that needs to be done?

Thanks