So what is a princeling anyway? They are generally considered to be minor royalty, in the line of succession but not so close that they might inherit. Not without a great many princes disappearing through voluntary or involuntary exile (or death) anyway. Princelings are entitled to live in a castle, and are taught the secret signs and behaviour that marks their status to princelings and royalty in other castles.
In order to become a prince, the princeling has to move into the direct line of succession (see L). That means they are a son or grandson of the current king. People who were once in this position but have been passed by as the inheritance went from their brother to his son retain their title of Prince as a courtesy, as do Princesses.
A Crown Prince has been announced publicly by the king as his heir. This just allows the Crown Prince a few more freedoms to move about the realms as he wishes, and also gives him status to attend Councils, where he may also represent his king and make decisions on his behalf. If an ordinary prince were to be sent to a Council by his king he would only be able to act according to the instructions his king had given him, in writing, which would be inspected by other kings there. Other princes would not be allowed into the meeting.
This is interesting since Lord Smallweed allowed Princeling George into the conference they were holding on the Energy Drain. He would probably not have done were it not for the note from Prince Lupin and the Lady Nimrod. It is true that a conference is not the same as a Council, but it was uncharacteristically generous of him, and shows how important it was for Vexstein to maintain positive relationships with Buckmore.
Are females whose brothers are princelings called princesslings? No, sorry, they aren’t even called princelings as they are not in the line of succession. If their father became King they would then become Princesses, but only then.
What is it with Fred ‘needing’ something and it turning up? Prince Lupin does it too, but only for unimportant things, so he says in Princelings and the Pirates. This appears to be a gift that a genuine prince sometimes has. We’ll explore it more under X.
Finally, if we are talking about princelings in general, small p; if it is certain Princelings like Fred & George, or the series as a whole, it’s Princelings with a capital.