I know a Nathaniel who is gorgeous, and Nat is a nice straightforward abbreviation too. I also know a gorgeous Sebastian but his German parents think Bastian is a good nickname and I really don't think that will work in an English playground!
Given your girls names what about Rose, Amy, Amelia, Caroline, Phoebe?
Bastian or Basty - not good in the UK . The problem with Sebastian is its lack of nice nicknames imo - Seb/Sebbie is awful (and reminds me of sebacious, oily) and Bast/Basty is too close to bastard in English...
I like Cameron and Frederick. How about Quentin (Quinn), Alexander (Alex) or Tobias (Toby)? I also like Flora and Anna.