All I have to say is enjoy while it lasts - both mine have been like that in early toddlerhood - and they are certainly not like that now. As they developed they had greater emotional need iyswim??
Now, when they do get engrossed in something or other I simply sit nearby and enjoy

. I guess I always 'passed time' to a certain degree, as even when they were great at this it really was never worth starting something that needed a lot of concentration as even when they didn't need much they will still interrupt for something even now and again.
I got a lot of down time out of a tray of soil and cut grass, and a bucket of tractors. I sat and read magazines etc most of the time. Lovely. These days it is only a short matter of time before a tractor ends up round someones head

.
Def gardening as well though. Cue the tractors again

, and a bucket!!!