They can choose their physical age and are adults every now and then. Strangely, I would have expected Samantha, of all of them, to be the one who prefers to be adult, especially as she does not want Robert to have to deal with politicians (she knows he hates it), yet she always goes to meetings as a 12 yo.

Much later on, she interferes when that America wants to take over most of the world. She is asked to meet with the American president and the first thing she does is warn him that she is a butterfly. She explains, "Most people, if they see a wasp in their home, they will kill it. If they see a butterfly, because it seems so innocent and beautiful, they will open their windows to help it get out."

You missed the part, just before her birth, when the Samantha of 297 years in the future returns as a soul to meet the family. She tells Robert that even at that time she, and the rest of the girls, are still 12 or younger.

If Robert was ageing, maybe so would the girls, but he remains at 18 to 24 years old in appearance. I think that being able to stay as young as they wish, while remaining in perfect health, means they release many of the fears that dictate how we think...so, how would that change them?

You could say the entire series of books are a series of experiments. How would people react to empathy; how would people react to being able to rejuvenate themselves; and so on. Of course, I also love seeing Robert being bossed around by little girls (I guess I would not particularly like it if they did so as adults, since I see enough of that in real life and those women tend to become too much like the communist fems of today).

:)

Staying or being able to stay young affects the way they think and behave, which gives the story another way of looking at life. Just think, in the bible it says certain people lived 700 to 1,000 years. If we all did, how would that alter our society and the way we think?

Finally - do not just think of them as children, for they do experience life and some of the pains - and remaining children does not entirely relieve them of the effects suffering can impose on our attitude.