No you don't need to reapply. If you have claimed it for your children you are covered. This article talks about people who have had a child but didnt register them at all for child benefit. Claiming child benefit (even if you opt out of getting the payment) gives you National Insurance credits if you aren't working.
My dh earns over £60k so rather than getting the money and then paying it back, I registered the kids with the child benefit office but opted out of getting the payment. I still get NI credits and the kids automatically get their NI number when they turn 16.