If kittens are afraid of new people in the house and do not go on hands, there is nothing strange in this, this is absolutely normal!
If you came to watch, show patience and understanding, cats are still wild animals and they need time to get used to a person, to his voice (especially a new one).As practice shows during viewing, adults often make contact with guests, and a little later, babies also connect to them. It all depends on the mood, age, character of the kitten. The little devon rex is focused on the mother, some make contact faster, others need more time - all devon rex are different.No need to bring treats with you, cats are fed certain foods, and the breeder is unlikely to allow them to give them incomprehensible treats. You can take a toy, a bow with you and try to use it for contact!