We have been doing this for a long time~ me getting a short workout at home, and the kids doing their exercises. You can see my mat crosswise just below where I am standing to take the photos.
I wanted to illustrate what it looks like to have three yoga mats for us in the edges of my bedroom. I have found that giving each person their own space works great.
You see that my younger son has a tiny kettlebell (I think it's 8 lbs.) and really light dumbbells that I bought for this purpose at Target (I bought him 2 pounders when he was really little and in looking here, I see he took what used to be my older son's 5 pounders) My older son uses my smallest kettlebell and smallest weights (16 lb. kettlebell and 10 lb. hand weights).
When they were really small, the little one used to jump in the doorway jumper and my older one would do exercises.