Ron's Kids names

[Robin]

No: HPFGUIDX 175844

I'm brand new to the group, so maybe this has been covered before and I 
apologize for then bringing it up again.

I don't understand where Ron and Hermione's kids' names come from.  
Rose and Hugo??  You would think that they would have at least named 
their son Fred!  

I suppose they don't HAVE to name them after dead loved ones like Harry 
and Ginny did, but....

Am I missing something?  Are Hugo and Rose in previous books somewhere 
and I've just forgotten?

Robin