T.N.
I wouldn't bother. We bought the Early Bird checkin last month when flying with our two three year old girls. Our pass numbers were in the A40s. There were people just a few behind us that had checked in at 24 hours.
But most importantly, if all you're worried about is sitting next to your kids, you don't need Early Bird. Families with small kids can board before the B group no matter what their boarding passes say. I think it's one adult per child, though, so not all six of you will get on early. But it's enough to ensure that your boys will have a family member to sit next to.