I take it you mean the cut off should be higher per household? i.e. £100k per household as apposed to £50k per person. As a single parent would be less likely to earn 100k than 50k?
It is not fair that a couple can have taxable income of 49k each and get child benefit, while another couple could have one earner with 51k taxable income and one with nil income and not be eligible.
Not sure a petition will change anything in the current political climate though.