For a kid, childhood is really important. What you go through as a child shapes your personality. Some people have miserable childhoods and spend their whole life healing from it, but others are lucky. Even if terrible things happen to them, they're able to deal with it in a completely different way.
Speaking of herself, the way her previous life turned out was definitely because of her childhood experiences. She'd been through hardship, so of course she didn't want her little brother to go through the same thing again. Otherwise, what's the point of all her efforts to keep him around? If it's just to make him suffer like she did, then it's really not worth it.
And as for childhood, Fan Tianyu's personality is totally thanks to a good childhood too. Actually, she kind of envies Fan Tianyu for being so easygoing. Sure, he's not the sharpest tool in the shed and really doesn't have much sense, but somehow he always warms up the people around him, plus he's really responsible.
