My dad used to worry about me because I was still reading children's books well into my 20s. I didn't know how to explain it to him because I wasn't sure how to explain it to anyone else. But basically I like a good story, and when a story is good, it doesn't matter what age group it was written for.
There's another thing about children's books--unless you are reading the "problem" books which address things like teen pregnancy, drug abuse, etc., most of them lack the conventions that populate popular adult novels lately, which include sex, excessive violence, and enough abnormal psychology to slather on bread. It's like the old Oprah's Book Club, in which the book's lead character always was a woman who had, as a child, been a victim of verbal/physical/sexual abuse by her father/stepfather/guardian/trusted relative and who grows up to get involved with an abusive boyfriend/husband/lover and who is further verbally/physically/sexually abused by that person--or she has a mentally challenged child and a neanderthal of a husband/boyfriend/father/guardian who wants her to toss the kid into an asylum. I'm not making light of any of these situations. These horrible events go on every day--and I don't want to read about more of them.
And this is not to say that children's books that are not "problem" books don't have their share of hard knocks. There is death in Old Yeller and Bridge to Terabithia and A Ring of Endless Light, cruelty in Anne of Green Gables and Black Beauty, poverty in Little Women and The Five Little Peppers, personal challenges and threats in the "Dark is Rising" novels...well, you get the idea. But in general the children's book world seems to be free of the excesses that drown the adult market.
Which is the long way of saying I picked up the latest History Mystery, Betrayal at Cross Creek, today. This one takes place in 1775 among the Scottish pioneers in North Carolina, people who escaped Scotland after the defeat of Bonnie Prince Charlie, as did my father-in-law's family, and examines the problems arising between the Patriots and the Loyalists. Pretty good. Although I guessed what the clue was, I didn't realize until the heroine, Elspeth, did who the "betrayer" was. It's pretty surprising for a children's book, too.