Oh my goodness, I can totally relate! I used to go straight from my classroom, to go pick up my two kids from nursery school, to head home for the evening/night routine... dinner, bath, bed, pack everything up for the next morning, etc.... and my hubby used to work super late at that time so I was on my own for most of the evening... Oh my goodness, nearly wore me out some days... so you're not alone, I know the feeling well!
Anyway, for me music was a totally sanity saver!
You mentioned you pick your son up immediately...Do you have any commute time at all between work and picking up the kids?? Can you leave work just a few minutes earlier so you have a buffer in between end of work and pick up time? If it is even just five minutes, you can give yourself a mental break with some music. If you need a "cool down after a tough day", try playing your favorite relaxation music or if you need to get pumped up for "the second shift" (with your kids), then try playing your favorite sing -out-loud kind of songs. I found that singing out loud was the easiest way for me to get my mind off work and off what was coming next. I'd sing even walking down the street (garnered a few stares :-P LOL but I didn't care... I was in NYC where people do crazy stuff walking down the street all the time anyway
)
And as for the kids, music helped out with that too. I played three kiddie dance songs when we got home so my kids and I could just be silly and laugh together. It was always three songs so they knew exactly when we would stop so there were no "more, more, more" arguments. And it gave them enough attention/time that they needed so they would then leave me alone to prep dinner after that. Next I played "quiet time music" (soft quiet mostly classial stuff) and they lounged around with their lovies while I prepped dinner. Most of the time they were wiped out after their day too so chilling quietly actually worked out okay.... Then we ate dinner and did bathtime (kept them both quick and simple)... and then finally I played the same lullaby CD at bed time every night. They were so used to that CD that the minute the first song started playing they were pretty much asleep.
Then I had some precious "me time". *sigh* and that's when I could really unwind or just fall asleep! :-)