Rihanna Struggles Juggling Working Out with Infant Son in Her Arms

Rihanna's learning motherhood is all about multitasking -- something her son reminded her of as she tried squeezing in a workout, with him riding the human equivalent of shotgun.

The singer posted a sweet home video of her at the crib with the kid -- whose name we still don't know ... but whose face we're certainly getting familiar with as time goes on. The 10-month-old was being held by his mama, and it looks like he was a little fussy in her arms.

In the video, you see her boy squirming about as Rihanna cradles him -- but, before long, she's got him distracted with what sounds like a family-friendly TV show of some sort. That seems to have done the trick ... judging by his big smile and cute cooing.

You can also see Rihanna's growing baby bump here as well ... where she's carrying her second child with A$AP Rocky. Just like we saw at the SB, it's pretty noticeable -- although it's hard to say just how far along she might be at this point. Looks like she's in the second trimester.

Gotta hand it to Rihanna ... she seems to be quite the hands-on mother ... even amid her pregnancy. Her son's been tagging along with her wherever she goes these days -- including for an overnight photo shoot she recently did, where Baby Fenty was asleep on mama bear.

Ever since we saw the kid's face in full view in December ... she's been showing off her little man a lot more on social media, and the kid's absolutely adorable. No exception here either.