Well maybe, Anhun. But I wouldn't say that Lucy behaved very childishly in both LWW & PC. For one thing, Lucy is only just starting boarding school in PC which makes 6 a bit too young even in LWW, if you consider her babyish. I started boarding school after my fifth birthday, and found it far too draining at that age. I still needed someone to help me get my hair done, and like the bulgy bears I sucked my thumb. I hadn't quite got the hang of tying shoelaces, though I was still expected to learn to make my own bed.
I'd say that even two years later, I was still far too young for boarding school. Our cut-off period for primary school, as opposed to infants school is 8 or 9. By then, being sent to boarding school is far more realistic. And Lucy could definitely look after herself physically in both LWW & PC.
Children who don't go to pre-school, who stay at home until 9 or, may grow up differently to those who do, who are in long-term childcare, and whose school experience is merely a continuation of their pre-school situation. I've also heard that before WW2 that children were seldom as grown-up and sophisticated as they were to be after the finish of WW2, and even as late as the 1970's. I've also noted with the advent of school counsellors etc that there are different expectations of children lately than there used to be. The common expectation of school children, especially girls, up to the 1960's, was not emotional maturity but how much maintenance any child might need, with the ability to care for oneself highly prized.