With any changes, there will always be some people who are on the 'cusp' who will feel it's unfair, and it sounds as though you're in that situation , polotixmum , and I can see that in your situation you're going to struggle. Having said that, rising fuel and food bills are affecting us all, whether we have children or not.
I think the rub, for 'me, is that you just can't compare one adult working with both adults working- you're just not comparing like with like. The petition mentions higher tax payers who have a partner staying at home. In those situations, there is at least the potential for the other adult to work. With one parent being a higher tax payer, childcare should be affordable with one child. In bigger families, there is the option of the second parent doing evening/weekend work if childcare bills are a problem. Whereas in families where both parents work , and neither is a HR tax payer, they are already both employed and spending a good deal of their taxed income on childcare already. There isn't the luxury of a non working parent to do some extra hours in the evenings to make up the loss of child benefit.
If there was an endless money tree- great, keep CB as a universal benefit. Seeing as there isn't, I would far rather see families with both parents already working but not on great incomes, being protected, rather than families who are already in the relatively advantageous position of having a HR tax payer and a SAHP. I have no personal axe to grind here btw- we both work but pay HR tax so will lose CB. I'll miss it, but I can see that working parents on lower incomes need it more