Define bright.
I know people with First Class Degrees who have come out with classic lines like, "Well penguins are fish anyway". Said with complete seriousness and honesty.
They might be academic but they are, in my opinion, as thick as pig shit, unless they have studied it and learn it by heart and can splurge it out in a exam. They are just good at repeating stuff once they have memorised it.
They lack any awareness of the world and they lack the ability to think for themselves.
Equally, you might be as thick as cow dung yourself so when your child can add 3 + 2 at age 6 without the aid of a calculator you might think they are bright because compared to your standards they are streets ahead of you.
In short, its all relative and depends on what you are actually trying to measure.
On another note, you are less likely to have a parent say their child is average than bright or has learning difficulties. Average is really the thing that everyone avoids saying, because that seems to suggest that there isn't a reason for their mediocrity and how they don't stand out from the crowd in some way.
Oh and IQ tests, don't measure intelligence in the way you think. They measure how good you are at doing IQ tests under those particular conditions. They don't take into account certain types of intelligence and they don't take into account how you may be affected by the conditions under which you might take the test (you might be a person who is anxious under exam type conditions for exam but might otherwise thrive under more 'natural' conditions even though they might be high stress situations).
Not to mention you might have an exceptionally high IQ but because you are useless at reading and responding to other people, its about as useful as a chocolate teapot as you can't use this intelligence in a way which is helpful and ultimately productive because you lack skills in other areas.
Emotional intelligence is essential to being bright in my honest opinion. You might not be academic but if you have the ability to do the most with what you have got and use it in a way that can achieve more than your 'more intelligent' peers, then surely you are brighter than they are?