i agree with amy...its up to the Holy Spirit to change their heart. right now, with the ages they are, i feel like maybe it is almost more appopriate to be concentrating on their salvation even more than their behavior.
i don't have kids that old, so i don't pretend to know how it works...but i do know one thing: when ministering to unbelievers (which i think we have to assume all children are until they have accepted Christ as their Savior), i am more worried about getting them to the feet of Jesus and letting HIM work on their heart than i am about changing their outward behavior. just my 2 cents.
please hear this: it may seem like your boys have a worse sin nature than others, but that is because you are around them every day and you see EVERYTHING. trust me...if you could see my heart...the way i speak to my daughter some days...the way i don't pray ferevently for some of my unbelieving family...the way i gossip...the way i talk back to my dh...etc etc etc. they are no worse than you or i....they just haven't wrapped their arms around Grace yet.