I KNOW HOW YOU FEEL!!!!! I too, could have written that post. I have 2 doing school work and 2 toddlers. I feel the exact same way. What I tried to do towards the end of last year and will try again (we took summer off) is to give the lots of cuddle time first thing in the morning. I try to be deliberate about couch time with them before we hit the ground running on school. Then before nap I cuddle them again. I'm not talking large chunks of time, just a little time that is devoted to the littles when I'm not distracted.
I know they aren't getting as much of my attention as my two big kids got as toddlers, but they know they are loved and don't seem to be suffering :) If they get extra whiny or fussy I know they just need a few minutes of Mommy time and then they are off and running again.
All that to say, I understand and I'm listening in for good ideas too!