Question

Why did mr. And mrs. Bramble hide the real identity of mr. Bramble from harold

Answer 1

The only reason is "society and rumours". Being human a social animal,he follows society . People filled fear in their mind that if Harold will come to know about his father's profession he wil get sad,but it's not true and we can see it in chapter further

Answer 2

Mr and Mrs bramble thought that Harold would think his father as a mean minded person...or lower class person so they didn't tell him