Part I:
I think that many of the characters in The Secret Garden could be considered good role models. However, this is not until the garden changes their lives for the better. Colin Craven, the young disabled boy, is an extremely gloomy and depressed individual due to his circumstances; however, with the help of the garden and his interactions with Mary, he starts to become more optimistic about the future, and has a lot more fun.
Mary Lennox, though she is an incredibly selfish and self-absorbed character in the beginning, seems to take a dramatic change in her behavior as she gets to know Colin. Her telling of stories to him is meant as a kindness, to distract him from his own troubles, and she gives him access to the secret garden, which starts to miraculously heal him.
The real role model from beginning to end given to us by the book is Dickon Sowerby, the younger child who is always sprightly and full of life. Martha, his sister, is also very kind and charming; her pragmatism combined with Dickon's optimism and energy make them both ideal role models for children. Mary actually admits that, " if an angel did come to Yorkshire," it would be like Dickon, noting how kind and cherubic he could actually be, as well as in reference to his love of nature. This makes them incredibly inspiring figures, and one that children could emulate; we even see this effect they have on Mary and Colin, making them better people too. Is it better to have a role model who is flawed themselves, and learns to be better (like Mary and Colin), or show perfect people from the beginning making others better?
Part II:
In answer to your question, I fully believe that Archibald Craven and Mary's mother paying more attention to their children would have made Mary and Colin turn out much better from the beginning. The relationships between these children and their parents are central points of the book, as Mary's and Colin's character flaws are shown to be a direct result of their parents' ignorance or attitudes surrounding them. Archibald's mourning and Mother's frivolous ignorance of her to care for herself seem to be reflected in their children; Mary is also self-absorbed, and Colin's depression mirrors that of Archibald's. It is only through the refreshing presence of the Sowerbys that the children, and eventually their parents, experience new sources of happiness and elation.
You make some very good points about the nuances of the parenting styles shown to Mary and Colin. Colin's father, Archibald, feels shame at his wife's passing, and the invalid nature of his son, and so he takes it out on himself. The idea of Colin trying to get his father's approval by not being ill anymore, which you point out, is very problematic in the book; should it be that children should work to be better than themselves to make their fathers love them? The same is true of Mary; if Mary became the kind of person Mrs. Lennox wanted to see at parties, would that make her spend more time with Mary? These somewhat troublesome undercurrents of the motives for these kids' improvements are quite interesting to think about, as they may not be turning into such selfless people as we might think.
Works Cited
Burnett, Francis Hodgson. The Secret Garden.