Why children are blind to imperfections of parents?!

Because they love their parents. Even children who are neglected, abandoned, or hurt still want the love of their parents and stay unbelievably loyal to them. They don't see imperfections because they don't WANT to see them. Only when they are much older, do many children accept that a parent may have acted inappropriately or in a hurtful way. But, even then, many will still make excuses for that behaviour/personality trait, rather accept it. I have worked with many children and I've been astounded at how forgiving they can be towards parents. Sometimes I wonder if we could learn something from them? A really interesting question and all the best with whatever prompted you to ask it :-)

Life and work experience

I say it's because it's before they're molded in to what society makes them. As a child, they've not really had much experience with the outside world thus all the things that will influence them are non-existent at their age.

The things that influence us is what makes us start to see the imperfections in everything else. With fewer variations in those influences, you have a more 'innocent' view of the world and see what your immediate influences are as perfect.

children are taught to trust thier parents. they follow thier every move and copy everything they do. while many outsiders can see the imperfections, the child is too young to understand that there is a problem. that is the last thing on a childs mind. they are thinking of playing or impressing thier parents. maybe the outsider should step up and intervene if they think the child is in any danger

I agree, it's because that's what the child is born into and that child doesn't know any better, then later in life you can see past the illusion and you can see what was wrong

trust me they're not... You'd be surprised how much a kid will pretend everything's ok when it's not but honestly they know.

personal experience

I'd say it depends on the child's environment and general personality.
I'm going to use myself as an example. I'm 15 and I recognize the imperfections of my parents very clearly. I'd go into detail, but a lot of it is personal. Basically, I know my parents better than they know themselves. That sounds like a grandiose opinion of my observational skills, but I have spent a lot of time analyzing them, their behaviors, categorizing patterns, digging into their histories...
I think the reason I can see their faults is because I tend to be quite observant, and I don't feel any emotional attachment to them. At all. I see them as a project, something to toy with...that sounds bad. I know.
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Most children don't see their parents' imperfections, mainly because morality tells them to obey their parents' every command and be completely dependent. When you're taught that your parents are basically replicas of jesus christ, you fail to see them as anything but perfect, until you become old enough to witness the faults of your parents.
Once the child turns 18 and moves out, spends a little time forming a life for themselves, spends time apart from their parents and has time to reflect, they then can form a more calculated opinion of their parents.