No basis for comparison

I wonder all the time what other kids are like.

I'm an only child, and while I had friends, I didn't experience what other kids in a family are like.  I only knew me.  I was advanced, at least academically.  Possibly a bit behind socially, but I seem to have caught up in that area just fine.

I also had no first cousins.  Neither my uncle nor my aunt ever had kids.  My mother's cousins had kids, but our families weren't very close, so I didn't have that close family relationship with them.

As an adult, since I was an only child, I could never become an aunt within my own family.  And my husband's only sister never had children.

I don't even have really close friends, or at least none that live nearby, to see their kids up close on a regular basis.

And my mom was self-admittedly not maternal.  I don't feel as though I can get any parenting insight from her.

So sometimes, it's hard to know what is ADHD and what is normal kid behavior.  And how to respond.

Is it normal for an 8-year-old/nearly 9-year-old to want someone to sleep with him?  (And how do you break that?)

Do kids get so doggedly set on something, like walking daddy to his car when the child is already in bed?  (And how do you respond when you can't convince him otherwise?)

What about a sudden obsession with getting a flute - but not getting lessons or playing it in the band?  (How do you convince him that you don't buy a real instrument that you don't plan to learn how to play?)

What are their sentences in writing homework like?  (And how can you help guide them, especially when they want help but don't want to hear anything you have to say?)

Do they refuse what you are serving for dinner, even something they like, and only eat a croissant?  (I know enough that you don't make this a big deal on a given night.  But what about if it becomes a pattern?)

Do they get angry when you tell them something they know, even if it bears repeating? 

How do you figure all this out without role models or examples?