I have to deal with this issue as well! I have 6 kids. (11,9,7,4,3,1) It can drive you CRAZAY!!!!!! You start your day off with a quiet time..."Lord, help me to love these blessings you have given me. Help me to teach them with all patience and kindness and love." OK....deep breath. Go out there and teach those little blessings! Then they start whining, fighting, arguing, and suddenly everyone needs to sharpen their 7 pencils that have ALL broke!!!!! It can turn the most patient, attentive mom into a frenzy. :)
I have realized it is all about consistancy! Explain and let them be assured that it is vital that they understand and work hard. If you feel like they are off in "la la land" and whining let's do an extra page for each time you whine! School could be out for the summer in a week at this rate!
Homeschooling is definetly a labor of love. I deal with this myself! Hope it helps! :)